Tournament poker differs from traditional cash, or ring, games in several ways. Most importantly, players are paid based on their finishing place in the tournament - and not on the value of the chips they have won. While most players will lose their entire buy-in, the few that finish in the very top positions will enjoy payouts many times their buy-in.
Since tournaments provide such a large upside for a relatively small and fixed downside, they are a very popular way for beginners to enjoy playing poker. And, as opposed to cash games which don't conclude with a clear indication of winners and losers, tournaments ensure there will be bragging rights.