The chakras are centers of energy in the subtler bodies, set along the spine like wheels. The word means wheel. There are seven main ones.
At the base of the spine is the root. Below the navel is the center of the creative energy. At the navel is the solar plexus, the center of feeling. In the middle of the chest is the heart. Then come the throat, the point between the eyebrows, and the crown of the head.
In most people they turn slowly, if at all. The tradition teaches that they wake as the creative fire rises along the spine, one by one, as the heart allows. With them come finer kinds of perception: intuition, true listening, inner sight.
The heart matters most. It sits between the lower centers and the higher ones, and the books say no higher center truly opens without it.
You have already practiced with the chakras. The five vowels of page 39 each vibrate one of them. The O, for example, vibrates the heart.
Gene’s free course Awakening the Chakras, in My Courses, gives each center its own lesson.