In Apokalypse each player gets a hidden card that gives him his game goal. There are two different cards, good and evil. The Good players can win all together, but only one Evil player can win.
On your turn you can play a population card, if you put it on the Good side you must give one of the cards from your hand to another player. If you put it on the Evil side you can steal a card from another player. You can also play cards to protect you population from the Apokalypse riders.
The game ends after the 4th Apokalypse rider.
The Good players win when all player's populations are more Good than Evil, and the Good players has scored more points than the evil players. The Evil player wins when the populations are more Evil than Good, and the Evil players have more points than the Good players, but only the evil player with the most points win.