Too bad this discussion forum is kinda dead.
I'm new to the creator as well and I'm also trying to make a multi-room level, which I take to be what you're asking about.
From what I've seen, you need to MANUALLY add wall objects and wall door objects to partition your room, then depending on whether your wall door object has a pre-existing door, you may need to manually add a door object.

This is the relevant part of an official tutorial video where they make a small cabinet whose doors can be opened:
https://www.youtube.com/watch?v=Y8p-C327wAw&t=442

In the case of room doors, the door objects come bundled with a pre-existing room key object (which you can position anywhere in the level) and the properly positioned logic object (where the key will fit to activate/open the door) positioned at the keyhole of the door.

If the wall door object already has a door in it you just need to reposition the key object.