A game mode is chosen before entering a world, and saving the world allows to take the Map into a new game mode from where it is left.
Survival is a game mode where you have to work to get everything in the game. It's the game mode where most achievements is unlocked. To prevent cheating it's not possible to take a Survival Map into another game mode and return to survival afterwards with that map. Big cities is not spawning to avoid giving players to easy access to materials.
Scenarios Its a map that resets when its finished so it can be used again and again. This game mode will host several PvP formats as well as puzzles and educational scenarios.
Designer Mode is a game mode where players have unlimited resources and access to stop the world physics and have the possibility to build and edit whatever they can imagine , using the Modelling tools.