A bet against the spread for the Bucks means you are taking their point total from the game, subtracting eight points from it, and comparing it to the 76ers’ point total from the game.
The plus sign before the 76ers’ spread number indicates they are the underdogs. The minus sign before the eight indicates the Bucks are the favorites. The spread here shows the Bucks as 8-point favorites.
We’re ignoring the total here, but it’s worth including because this is what you will see when looking for bets. A bet sheet for a game will usually look something like this.