Minecraft is an open world game with 3 different modes:
Survival- Competitive either multiplayer and/or single. You have to try and survive the night by crafting different mixtures, you also have to fight off various threats including zombies, creepers, endermen, etc.
Adventure- Just newly added includes different custom maps to survive and work through.
Creative- You are able to create literally anything you can imagine, you’re able to play alone or with friends.