A psi ball is simply a ball of energy in which you can manipulate in your hands
Shake your hands out for a couple of seconds, then put your hands close together, not touching, but 2 or 3 inches apart. Your hands should be flat, as if you were clapping, not as if you were holding a ball. Clear your mind, focus on only the energy in and around your hands. Picture electricity shooting in between your hands.
After a wile (not long, maybe a minute or less, it will happen faster with practice) you will start to feel the energy forming in between your hands. This will feel as if your hands are magnets. You can slowly pull your hands apart, you will feel the energy grow as you do, then you can slowly press your hands closer together, as you do, you will feel the pressure in your hands. You may not get it very well on your first try, do it a couple more times until you get it. It will get easier to make psi balls as you practice.