While I can’t answer the other question, as I periodically have the same problem, I can give you a quick door tutorial, so step on in– err… Door pun… Don’t be stiff (;D).
So, using doors is really easy. All you have to do is place them where you want, then hit the gear button on the menu where you found the door, and click on the door once more. Now that you see the options from this door, click on “To Scene” and select which scene you would like the door to access. If you have multiple doors in that scene, it is advantageous to, after selecting the scene, click on “To Door” and select which particular door you would like to access.
Hope that helps!