OK, so it looks like you confused the 'two worlds' with 'dream world' and 'nightmare world'. The two worlds are the real world and the dream/nightmare world.

When you're in the real world and your character falls asleep at night, they will create dreams for characters in the dream/nightmare world to explore. Does that make sense? So if you're in the dream/nightmare world, you can explore other character's dreams. If you're in the real world, you're making dreams for other characters to explore.