For sports like basketball and football, betting on the point spread is the most popular method of wagering. For an example, if a favorite is listed at -2.5, that team has to win by 3 or more points for you to win the bet. If the underdog wins or loses by 2 points or less, the underdog wins the bet.
The other popular method of betting is on the money line. Odds will be listed for a team to win. An underdog could be listed at +200, which means you’d win $200 on a $100 bet if your team wins straight up.