When you start a game, you can choose between 5 different game modes: survival, free, extreme, creative and custom.

• In survival mode, you have to find materials and components to craft items, and manage your oxygen level, hunger and thirst.
• In free mode, you also have to craft items, but you don't have to manage your hunger and thirst. However, you do need to manage your oxygen level.
• In extreme mode, it's the same as survival mode, but you only have one life!
• In creative mode, you have no more constraints: you don't have to manage your hunger, thirst, oxygen levels or pressure, and you can't die. Materials are not required for crafting.
• In custom mode, you can create the game you want and adjust almost all of the aspect of the game. Note that this mode prevent you from unlocking achievements!