You move with your mind through your body. And as you do so, you gently squeeze a bit each organ you contact. Now, each organ contains a certain amount of energy charge, which, as you sqeeze it, gets released. If you become aware of this energy, either through feeling or through perception, this is called vitakka (in Pali), application of mind to the fine-material. Most of the time, this perception of energy will last only a short time and then dissipate, and back you are in the material world. But as you become more ingenious, you may be able to not only sqeeze out some energy from your body and then notice the same, but also to manipulate that energy around a little – making it move like a dragon from your body; making two, three streams of energy come out of your body simultaneously and dance around each other, forming geometrical patterns; or making it turn into a protective sphere which surrounds you.
The sustained act of meditation therein is called vicara. The joyful playing with that light or energy is called piti-sukkha. And the perception of that light is called ekaggata, one (-pointed)-ness of mind. Thus does a possible playing out of the first Jhāna come about.
This play then will have to be played so well, that eventually it is playing itself out all by itself, just as if one were to move from a driver’s seat in a car to the side or back seat, where one can begin to enjoy the beautiful scenery and be glad with just the simple feeling of vibration and movement of the car. This will be the experience of the second, third, and with greater refinement, also of the fourth Jhāna. After that, the mind is so alert, subtle and unified, that the perception of the scenery begins to stimulate the imagination, and the journey of working with the light will give way to a journey of working with the mind.
A journey for which some other materials on this webpage may be of use to you. For that, you may check out the middle portion of the blog post “Keys to the Abhidhamma system”, or the post “A small outline of consciousness”, or any other post under the category of mind.