How to make houses so one can enter them?

I've been working on my first level for quite some time now and I need help with houses.
How do you make them so you can enter them? I've been working on a city area lately and really want the houses to be enterable (spelling?) Anyways, thank you in advance.

You need to use shifts for them. Note that you can only have up to 3 shifts on one screen, so only 3 houses (doors) will be accessible at a time.

A shift will warp you to another screen when pressing down. See the [faq] for more info. It'll tell you how to use the editor, which'll point you to this: http://nifflas.lpchip.nl/index.php?topic=18.0

Thank you alot. This definatley helped me.