This time start with one ball in each hand. Toss the first ball, as before (you did perfect the toss, right?) As the first ball reaches it's peak (approximately eye level) toss the second ball underneath the first with the same scooping motion, and then catch each ball in it's respective hand.
Make sure you are not tossing the second ball over the first, as this would be a reverse-cascade, which you may learn later. Also, be sure you're not passing the second ball directly to your other hand, this would be a shower pattern, and it is significantly more difficult than a simple cascade.
Practice this, alternating the hand which makes the first throw, until you can do it five times in a row without a drop.