There are many techniques in use for throwing pots, although a typical procedure is:
Put a round, moist ball of clay body down onto the bat (batterboard) with a little water or small amount of clay smoothed over the area to hold it in place
Center the clay body on the wheel by applying pressure with a wet hand on one side and the other hand on the top, allowing the clay to pass through the hands. An alternative to this is to 'pull' the clay body up and down until it is centered
Find the center of the clay by moving a thumb or finger across the clay until no more friction is felt as it turns