Online scratchcards are the digital version of the ottery scratchcards usually purchased at conveiniences stores and stands. Playing scratchcards online you click in designated areas of the scratchcard and reveal the hidden information to unveal the scratchcard's prize value. The chances of winning are determined by the live game provider and they may vary.
Since you can't use either your fingers or a coin to scratchcards, what do you use when you play scratchcards online? You use the mouse, and by moving it into designated ares, where you scratch according to your preferred method.