Verified answer

Anything you want. Explore, mine, fight, and much, much more. What you do is up to you. You can create things in creative and you can try to survive and beat the game in survival and there is so much more that I can't even put on here.

Craft, build, tame mobs (and kill them), there are tons of answers, here's where it tells you almost anything about Minecraft: http://www.minecraftwiki.net/wiki/Minecraft_Wiki