Rebuy tournaments have become increasingly popular, and most online poker sites now offer them. Usually in a rebuy tournament you are allowed to rebuy until the first break, so normally for the first hour. Some poker sites will limit how many times you are allowed to rebuy, while others will allow unlimited rebuys. After the rebuy period ends you are offered the chance of purchasing an add-on, which you should always take because the extra chips will increase your expected value in the tournament.
Don't be afraid to go all-in in the early stages of the tournament, because you can always rebuy. You will notice maybe 5 people could all go all-in for one pot, simply because they know they can rebuy and try again, but you don't want to be wasting all your money rebuying and then not cashing. Here is some advice on how you should play in certain stages of a rebuy tournament.
In the early stages you should adopt a very aggressive style. Players will go all-in with almost any hand in the early stages, therefore if you get a big hand and go all-in it's very likely you will be called because they won't put you on a big hand ? they will think you are like them, betting with marginal hands because you can rebuy if you lose. Unlike most poker tournaments, coin-flips are okay in the early stages of a rebuy tournament. Your aim is to build your stack; therefore you must risk your chips to win some. However moving all-in every hand isn't going to get you very far; it will just cost you a lot of money constantly re-buying.
There is a big difference between playing aggressively and playing stupid. Going all-in with a hand such as A-3 will more than likely be dominated pre-flop because your will have quite a few callers and your opponents will be going all-in with any Ace, leaving your kicker way behind. After the rebuy period you will have the option of purchasing an add-on. All good players will purchase the add-on, simply because it gives them more chips to play with - meaning they can win more. After the first break and rebuy/add-on period the tournament will start just like a normal tournament, so you should now adopt your normal tournament strategy.
If you have a big stack then you are in great position and should look to build it playing your best hands aggressively, and pressuring the short stacks. If you are a short stack or just below average then you should avoid the large stacks who will most likely call you with anything to try and get rid of you. You will really need to double, or even, triple up to have any chance of making progress and having a chance of winning the tournament. Rebuy tournaments can be very profitable for tournament players. Let's say 50 players enter a $10 rebuy tournament, that's $500 in the prize pool, but if 10 players rebuy then that's another $100 for the prize pool meaning there is now $600 in the pool.