you can only access levels that you have taken over. To take over a level you need to attack it and in order to do that you need to be on a level thats connected to the level you want to attack.
Attack - just takes over a level if player is on a connected level
Go - Changes currentLevel to selected one if its taken over
Gold level = currentLevel
Blue level = Level is taken over and can be set as currentLevel
White level = selectedLevel