Every slot machine will include a pay table. This is a table of all the potential prizes that could be won while playing that game. It shows you which combinations will produce prizes and how much you will win for finding each combination on the reels.
Some pay tables consist of just one page if the game is a simple one. Others might be included on the game screen itself. This is more likely if the game is a simple three-reel one with minimal prize possibilities available. If the game has five reels and multiple paylines, the pay table will appear on another screen. This will be accessed via a logo or help button on the screen.
Some pay tables may consist of several pages too, especially if there are lots of bonuses included in that game. The rules will be explained there, along with the format of paylines or way wins that are included. In short, it is best to view the pay table prior to playing any slot game, as it will explain how the game works and how you can win prizes.