Games with a single payline will only pay out if you get a winning combination across the middle of each reel (Some symbols will pay out if you only get one or two of them, but they must still be in the middle of the reel)!
Single Payline games will sometimes have bonus features, or a special jackpot that you can win if you bet more than one coin. The Pay Table shown on the game screen will tell you what this is. In the pay table in the example below, you can see that if you bet 3 coins, the jackpot is more than 3 times as much as the payout if you had only bet 1 coin.
You can specify how many coins you want to bet on each spin, either by clicking on the column you want (in this case Coin 1, Coin 2 or Coin 3), or by using the Bet One and Max Bet buttons at the bottom of the screen.
Remember: you can change the value of the coins you are using if you want to bet higher or lower amounts!