When you're playing a card game like poker that involves betting, each player takes turns making bets. When one person bets a certain amount, everyone else must either "see" the bet, which means to bet the same amount, or "fold", which means to give up and lose that round.
So when telling a story about a poker game that you played, you might say:
I wasn't really sure what to do, but I saw his bet. It turned out that all he had was a pair of aces.