What is a Swiss tournament?
A Swiss tournament is different than a Round-Robin tournament in that no players are eliminated. Every player will play every round, and the player with the highest number of points at the end of the tournament is the winner.
In a Swiss tournament, you don't necessarily play every other player. If there are a lot of players in the tournament, there may not be enough rounds for everyone to play everyone. Pairings try to put together players of similar rating. Because of this, the highest rated player might not always be the winner, and a lower rated player who beat all his opponents (who would be of similar rating to him) could end up winning.