The line is expressed in terms of points, and the favorite team is listed with a negative number next to its point spread. The underdog team is listed with a positive number next to its point spread. For example, if a team is listed as a -7 favorite, that means it is expected to win the game by 7 points or more. If a team is listed as a +7 underdog, that means it is expected to lose the game by 7 points or less.
If you bet on the favorite team, you must win by more than the point spread in order to win your bet. If you bet on the underdog team, you can either win outright or lose by less than the point spread in order to win your bet.
The line can also be used to bet on the total number of points scored in the game. The over/under line is set by oddsmakers and is based on a number of factors, including the teams' offensive and defensive statistics.
If you bet on the over, you must predict that the total number of points scored in the game will be more than the over/under line. If you bet on the under, you must predict that the total number of points scored in the game will be less than the over/under line.