As you might guess, a reverse scramble is, well, the reverse of that: the worst of the tee balls is chosen, and that's where the second shot is played. The worst of the second shots is chosen, and the third stroke is played from that location; and so on, until the ball is holed.
We strongly recommend against using reverse scramble as the format for a tournament. This game requires many more strokes to complete a round, and takes a lot of time to play for groups of golfers.
Instead, treat reverse scramble as a practice game. Play it when you're on the golf course alone, hitting two balls off each tee. Or play it against one friend in a twosome, with each of you hitting two balls on each hole.
Because of the added time a reverse scramble adds to a round, it's recommended that you play it only when your course is uncrowded and golfers behind won't have to wait on you.
Reverse scramble is a good practice game because choosing the worst of two balls will allow you to hit many more shots of different varieties, shots you probably don't otherwise practice very often.