The main goal is to reach the The End dimension, but it is all up to the player what the real goal is.
The player will spawn inside a chamber with a small amount of portals.
Each portal is a one way dimension. After wandering around the portal will be deactivated. It gives time for the player to choose the home dimension since some can cause game crashes and/or photosensitivity triggers.
The player can return to the portal hub whenever going to the reset dimension: The Nether.