There are many different kinds of holding a ball. The easiest way is to feel that you are holding a ball in your own two hands. The ball may become larger or smaller and your body and hands can move by following the strength of the ball, up and down and move around. You can also practice with music and follow the melody or rhythm, just like you are dancing. This method is the practice where Qi is staying outside of the body.
When the ball is held inside the body, it is a different method and feeling. This is a more profound and advanced Qigong practice. Normally, we start to practice the method with the ball outside of the body and then make it go into the body gradually.
The more difficult practice method is holding the Tai Chi ball. It needs a long period of practice to truly understand the various features of Tai Chi ball as well as the actual functions and techniques. To know how to use Tai Chi ball is a big task.