There are 2 stages in TUS cups: first off, there's a group phase, where everybody plays everybody else in their group. The games there are bo1 in this cup (bo1 = best of 1; the first person to win a round, wins the game)
After that, the winner and runner up of every group qualifies for the knockout phase. You play your opponent and whichever wins, goes to the next round. The loser is out. The games in the knockout phase are bo3 in this cup (bo3 = best of 3; first person to win 2 rounds wins the game. It's named like this because you basically play 3 rounds and the winner of these will have either 2 or 3 wins)
