A point spread (or line) is a tool used by sportsbooks to attract wagers on both sides of a game. The line is most commonly used in football and basketball games. Because it’s rare for two teams in a pro sports game to be completely evenly-matched, one team will have an advantage, another will be seen as the underdog. The point spread is the handicap offered to the underdog to level the playing field, so to speak.
In this instance, the Dodgers are the favored team, as signified by the negative numeral. It would cost you $130 in order to collect a $100 payout on a Dodgers victory (plus the original wager of $130). But if you bet $100 on the Cubs, you'd collect $120 if they win (plus the original wager). In other words, you'll have to wager more money on Los Angeles than you would Chicago in order collect $100 on a bet.

In this example, we have a favorite to win, and an underdog. The Packers are the favorites, and that is shown by the (–) value in front of the 6. Underdogs are represented by the (+) value.  The 6 point value is how many points either team could win, or lose by. If you think the Packers will win by MORE than 6 points, then you’d bet on the favorite in this case, meaning that the Packers have to win by 7 or more points in order for you to win your bet.