The words Samatha, Samādhi and Jhāna are mostly used synonymously. They all mean Concentration.
"Samādhi" literally means "placing firmly together (sam-a-dha). The word "Sammā-samādhi" is one of the mental factors of the Noble 8-fold Path and was used by the Buddha himself.
Jhāna corresponds to the Sanskrit "dhyana", and is derived from the root "jhe" which means "to think" or "to meditate", namely, to think closely or meditate firmly upon a given object. Jhāna is both a system of mental training and a process of transforming the lower states of consciousness to higher levels.
In the Second Basket of the Scriptures, namely, the Suttas, there are 4 Jhānas, but in the third Basket, the Abhidhamma, there are 5 Jhānas. They are practically the same; in the Suttas, the first 2 of the 5 mental factors have been coalesced.
The main idea of concentration is to fuse the subject and the object, and this is achieved at the higher levels of consciousness. At first, concentration is helped by the will.
There are two separate levels. At the bottom it is calm, whilst at the surface there is discursive thinking. The practice of concentration calms the surface.
The general idea is to transcend the Sensuous Realm bringing the Mind to the Realm of Pure Form, and then later to transcend the Jhāna Factors of Applied Thought, Sustained Thought, Joy and Bliss till one attains perfect one-pointedness of Mind and equanimity. The last is reached in the 4th Jhāna.
Your decision to concentrate is the important step. It means that you have the desire and the will to get rid of your worries and your fears and your restlessness, as the case may be, the difficulty with most people is that they subconsciously enjoy being worried and being restless.
Concentrate on your in-breaths and out-breaths at the tip of your nose. Whatever you may be doing or not doing, your subconscious carries on with your breathing, and it is a simple matter to concentrate on something which occurs automatically all the time.
Sit down quietly on a chair and concentrate on your in-breaths and out-breaths. The best place to concentrate on your in-breaths and out-breaths is at the nostrils, but you can try the alternative of concentrating on the rise and fall of your belly as you inhale and exhale.
If you have the time and the inclination, and you want to concentrate for more than half an hour, it is better to sit cross-legged in the "Turkish Fashion" on a divan or on the floor. Sit with your legs stretched out, and then bend your left leg at the knee and place it under the right thigh. Then bend the right leg at the knee and place it under the left leg. The position of the two legs may be reversed. If you are very uncomfortable at the start, sit on a low stool or a book or something, 2 or 3 or more inches high.
When sitting cross-legged in the Turkish fashion, one shin is over the other; in due course there may arise some aches and pains where they touch or overlap.
A better cross-legged position is when the two shins do not touch at all, but it is difficult at first. When on the floor bend your left leg as usual, bringing your left heel towards your body. Then manoeuvre the right leg so that your bent right leg does not touch your bent left leg. This is easy if the junction of the thigh and the shin lies flat on the floor. Actually, if at first this junction is higher than the floor by a few inches after some months of trying out this posture, one day the junction will lie flat on the floor. At the same time the junction made by your right leg will also lie flat on the floor. The position of the two legs may be reversed.
You should be able to concentrate for hours and hours without cramps and aches, and this is possible by assuming a correct posture.
Concentrate on your breathing. Let your subconscious direct your breathing and you are just to be aware in the first instance whether your in-breath is long or short, and whether your out-breath is long or short.
As an aid to concentration, you can count your breaths, 1. (one) for the first in-breath, and 2. (two) for the first out-breath, and 3. (three) for the next in-breath, and 4. (four) for the next out-breath, and so on up to 13 or so. You can repeat this for a number of times till you think that your mind has become somewhat calm.
Now you can concentrate on your in-breaths and out breaths at your nostrils or the tip of your nose. Keep on concentrating for as long as you want, or for as long as you can.
It may be better for you to begin with short breaths, not very short, but more short than long. It takes some doing. It is more difficult than you think. Before you can get some sort of concentration, your mind has gone elsewhere, and you have to bring it back to where you started.
It is better to consider that there are two zones of consciousness or awareness, namely, the focal zone where your mind is in proper focus, and the marginal zone where you are aware of something somewhat in the background and where your awareness is a bit out of focus but you are aware of it all the same.
It is sometimes said that it is not correct to say that there are two zones of consciousness; the mind works so fast, in less than a billionth of a second, that there are really two different successive minds, but you think there is only one.
Whatever it may be, try this exercise. When next you drive your car, be aware of whatever you are doing as you drive your car, but also in the marginal zone of awareness be aware of your breathing in and out. Do not think of anything else except your driving in the focal zone of your consciousness and of your breathing in and out in the marginal zone of your consciousness. You will be surprised how much more alert you are; you will have become a much better driver.
During the day when you are performing any task, perform the task with the focal zone of your consciousness, and at the same time be aware of your in-breaths and out-breaths in the marginal zone of your consciousness. You may have some difficulty at first but you will come to enjoy this concentration exercise as time goes by.
At first there are 3 thoughts, the first is the thought of the in-breath at the nose-door, the second is the thought of the out-breath, and the third is the contact at the nose-door. Later, these three thoughts are merged into one.
Even if you start with short breaths, the breathing eventually goes into long breaths.
After some time, the breathing apparently ceases. You cannot say whether you are breathing or not, the breathing is so refined and delicate.
You must make an effort to maintain rhythmical breathing.
First there is what is called "Preliminary Concentration".
The objective is the suppression of the 5 Hindrances which are impediments to good concentration, namely:
Craving for sense-pleasures; kāmacchanda
Ill-will, vyāpāda
Sloth and torpor; thīna-middha
Restlessness and worry, uddhacca-kukkucca
Perplexity and skeptical doubt. vicikicchā
They are defilements which are hostile to the clear mind, and therefore must be suppressed; otherwise the mind will not be concentrated.
They can only be suppressed at this stage and cannot yet be eliminated. It is only after achieving the First jhāna, and thereafter, that they are automatically eliminated.
When your concentration is getting better and better, and you have Basic Good Conduct you will get your Sign.
This sign is different to different people. To some it is like a lotus, or a round jewel or pearl, to others like a column of smoke, the sun, the full moon, starshine, a silver gridlechain, a garland of flowers, a spreading cloud.
Once you get the Sign you must concentrate on it and leave aside the breaths and the "nose-door".
The sign must now be carefully guarded and fostered. It must me made to grow at will.
You must now be careful of the company you keep and not mix with persons who are not spiritually inclined.
You must be careful of the kind of talk you indulge in, for talk is the result of thoughts.
You must avoid useless and aimless talk, as otherwise your included image will disappear.
You must also take care of the food you eat to ensure that it is not unsuitable and cause you bodily trouble at this stage of your mental development.
You must also now try and see whether it is better for your concentration when you are sitting or lying down or standing walking.
At this stage it is best to delimit the size of the induced image. It’s no use having it too large. Enlarge the induced image to any size you want, but don’t have it too big.
When the 5 Hindrances have been suppressed simultaneously, Ecstatic Concentration is obtained. This is the First Jhāna. This is when the Super-conscious Mind takes over.
With the First Jhāna, you have the Jhāna; factors of Applied Thought, Sustained Thought, Deep Interest or Joy, Bliss and One-pointedness.
This complete absorption transcends the Realm of Sensuous Desire, and brings you to the Realm of Form. You are now ready to proceed to the Second Jhāna.
The Second Jhāna is attained by transcending applied thought and sustained thought.
When you have attained the First Jhāna and obtained proficiency therein, you review your achievement.
You feel that your mind is not quite so calm, disturbed as it is by waves of applied thought and sustained thought. The latter are gross in nature and you are threatened by the 5 Hindrances.
At this stage you require personal confidence and great exaltation of mind.
As concentration proceeds, you will now experience joy which refreshes the mind and body.
There are many forms and intensities of joy, ranging from the joy that raises the hair of the body, to the joy that raises you off the ground, sometimes to the ceiling, to the joy that breaks over your body like waves on the seashore, to the joy which is all embracing and suffuses both body and mind.
With all this joy of excitement, your body will not be tired. You will feel light as you are refreshed.
You now make a big attempt to transcend Applied Thought and Sustained Thought, and you attain the second Jhāna.
Emerging from the second Jhāna, you review its factors with self-awareness and mindfulness. You are aware of its defects and that you are threatened by Applied Thought and Sustained Thought.
The joy you have experienced appears gross, whereas Bliss and Concentration make for peace of mind.
You must transcend Joy whilst remaining in equanimity of Jhāna, which is like indifference or disinterestedness. You are unaffected by pleasure or pain.
If you are not careful, the mind will return to Joy again.
You continue your concentration on the sign or after-image.
As soon as Joy is transcended, Bliss together with Concentration is achieved and you have attained to the third Jhāna. You are now blissful and evenminded.
You are still threatened by Bliss. You are therefore to transcend Bliss.
You keep concentrating as before. You become free from both pleasure or pain, either physical or mental. There is a difference in this world between physical and mental pain. Whatever may be your spiritual development, you will experience bodily pain till you die, but when you have attained to great spiritual development, there is no more the feeling of mental pain.
You now have a neutral feeling, of neither pleasure nor pain.
You how have the purest mindfulness through equanimity. There was a vestige of equanimity before in the previous stages of Jhāna, but now it is manifested to the full.
There is now perfect equilibrium of the mental states, which is the ultimate aim of Jhāna. You are free from all kinds of mental disturbances. You are serene.
You have now achieved Perfect Concentration, with perfect stillness of both body and mind.
It is ecstatic concentration you have achieved the fourth Jhāna.
At this stage you have achieved supernormal psychic powers of clairvoyance and clairaudience and of seeing the auras of others.