Just keep chomping until you get caught. Utter simplicity with a huge impact on the game industry.
I remember being three years old playing Pac-Man and calling the dots oranges instead, as it seemed to make more sense at the time, and the power pellets as medicine tablets for power to be able to eat ghosts safely. The ghosts would chase around Pac-Man with each ghost with different interactions toward the player's actions.
In the game you try to survive as long as you can in levels of increasing difficulty. Sound familiar? Pac-Man is actually one of the first instances of a "hold out as long as you can" type of game. Plenty of games have been inspired by this concept. From tower defense to first person shooter survival modes.
Pac-Man's simple concept is highly addictive and has remained popular over the years with games constantly being inspired by it. It's impact was huge in gaming.