It's an individual skill that teaches ball and body control. Let the player pick up the ball to start.
More advanced players can flick the ball up to begin.
It's okay to initially use the hands. Start on the thighs. A larger surface is easier than smaller body parts. Move to the feet - once players get a feel for the activity, the feet are the next logical move. A player can alternate thighs and feet or juggle with one thigh or foot at a time.