There are several formats to tournaments. I guess the two most common are those I List below:
You enter the tournament and are given a number of chips equal to those given to other entrants. You play in one of many qualification rounds and the top chip holders progress to the next round. Maybe the top one or two from each table progress to the next round. Eventually, (usually after a qualifying round, quarter final round, semi final round) the players have been eliminated so that only 6 or 7 are left standing. Whoever wins that final table is of course the winner.
The other format is similar but the qualifying rounds progress the top one or two players from each table. The rest of the tournament is played like the other format with quarter final, semi final and final rounds.
In both formats that I've encountered, there are a set number of hands that are played. 21 to 30 hands seems to be about what they all choose to go with. In some of these tournaments, there is a maximum bet that can be wagered with the limit removed for the last hand and sometimes, the last two or three hands.
Of course, there are about 1,437,865 different ways a tournament can be formatted <smile>.