Almost all point spread wagers are paid out at moneyline odds of -110. This is almost even money minus the percentage that is taken for the sportsbook's cut known as the vig. Sometimes you will see a bit of variation in the payout odds, but for the most part, you should expect to see -110. If you don't see the payout numbers posted but just the point spread, you can most likely assume that you are to interpret that as being paid out at -110. If you're ever curious, though, just ask for clarification or look at your betting slip.
Sports betting has been around since 1000 B.C in China, where betting on animal fights was commonplace. In ancient Rome, one could wager on the Gladiatorial games. The idea of betting on sports is as old as organized sport itself. But up until the 1940s, bettors were fairly limited in what kind of bets they could make. The standard system of odds would allow bets on, for example, the 3-1 odds that the Steelers would beat the Browns.