Ah, Pacman ... The classic among classics. Is it still needed to introduce this arcade game? Probably not, but let's explain the principle anyway.
In Pacman games of your hero is a kind of yellow pie that need to eat pellets (and eat all of them!) without getting caught by the colored ghosts that lurk around. Sometimes you can eat pills or fruits, which make you become overpowered within a few seconds which enable you to eat the evil ghosts. Levels are more and more difficult.