Is basketball the only sport you want to learn to bet on?
If a team has a - that means they are favored to win the game by the amount of points the experts who make the number start it at. (-3)
The opponent is the team favored to lose by the same amount of points (+3)
So let's use this example:
Indiana Pacers -5.5 vs Orlando Magic +5.5
If you think the Pacers will win by at least 6 points or more, then you want to put your money on them -5.5.
If you think the Magic will win the game OR only lose only by a few points less than 6, then you want to put your money on them.