First of all, you need to find a good set of juggling balls. For that purpose, you should consider using soft balls. Many people use tennis balls, or any other hard balls for the technique. However, it is not recommended for the beginners to practice directly with such balls. You can visit a nearby sports store and ask for the juggling balls.
Before you start juggling, you need to hold two balls in your left hand and three in your right hand. Throw one ball from your right hand, into the air, in a way that it should make a trajectory to fall into your left hand.
When the first ball starts descending, release the two balls in your left hand in a way that one ball should move to your right hand and the other one should go straight in the air and return back to the left hand.
Catch the first ball that you had tossed using your left hand. Now toss both the balls in your right hand into the air in a way that they should split and fall in different hands.
Catch all the flying balls, it comes with practise. After you are done with finishing one complete cycle, you will find that your left hand will have three balls and you will have two balls in your right hand. It means that the number of balls in both hands change after each cycle.