Only bet games where you have a clear prediction on a team covering the spread. Look for lines that you think are incorrect and put your money there. The idea here is to be making intelligent picks that you actually believe will win. If you're betting every game, you're just gambling and no longer letting your skill and knowledge base shine through.
Technically, probability should always be a number between 0 and 1. It's often expressed as a percentage though, which makes things easier for the purposes of betting. 0.7059 converted into a percentage (i.e. multiplied by 100) gives us 70.59%. What this means is that the odds suggest the Celtics have a 70.59% chance of winning. If we believe the Celtics have an even greater chance of winning, then we should back them at odds of -240.
As you can see, the public seems to think that Florida is going to win this game by more than seven points. If the game started now, the sportsbook would stand to lose a lot of money if Florida did in fact win by more than seven points. They would stand to make a lot of money if Florida lost or won by less than seven points. Regardless of how the sportsbook thinks the game will go, they are not in the business of gambling. They want to guarantee profit as often as they can.
That was all before Charles McNeil, a math teacher from Chicago, invented the concept of the point spread. An avid gambler, McNeil created what he called “wholesaling odds” and started his own bookmaking operation in the 1940s. He started out offering this new style of betting on football, but his business model grew to include basketball.  McNeil changed the way sports betting was done, and his legacy lives on today in what we now call the point spread.