say you join a tourney that has re-buys & add-ons. You start with say $1500 in chips...you can automatically re-buy another $1500 right then or at anytime during the set re-buy period whenever you get below the $1500 mark. And you can do this as often as you want during the re-buy period as long as you are below the $1500 mark.

At PokerStars, the re-buy period is up to the first break (usually one hour). During the break, if you're still in the game & regardless of your chip count, you can purchase an "add-on" for the same cost as the re-buys.

Steve B