Teleportation (Where to even start?)

First, I’m going to say this: I’ll be describing exactly what I want to make, but I don’t want anyone to go out and just hand it over to me. All I’m looking for is advice on where to START.

The end result should be as follows:
There will be 5 doors and one enemy. The doors will be one the stage, while the enemy will be added to the stage via code. The doors will all have an initial state of being closed. After a small amount of time I will change the state of all those doors to being open. When this state change happens, I want to spawn my single enemy in one of those doors at random. This enemy will then move around the stage (flying) based upon specific paths I set out (multiple paths, one chosen at random) and end their trip by flying back into one of the doors and be removed from the stage, with the doors going back to their closed state.
Rinse and repeat.

So, as I said, the main question is how do I even start? (Oh and done in external AS files).