You play a god, gaming against other gods in a celestial game of conquest. To win, you must help your chosen people take over the world and wipe out the vermin who worship that other god.
Each god starts out with a single human, dumped into the middle of the wilderness. Sometimes there is inhabitable land in sight, sometimes not. To get a chance to win, you must change the landscape, creating flat land for your followers to build on. The more followers you have, the more powerful you will be, so take care of them. Build as fast as you can, because the other god is doing the same.
When you have enough followers, you can make the leader of your people into a hero. He will then go around the land you have built, literally taking strength from the people into himself, and working his way toward the enemy. When he gets there, he will engage in holy warfare upon your enemy's people. He will burn; he will kill. And he won't stop until they're all dead... or he is.