Making a Custom Story

[FlawlessHappiness]

This is only my opinion:

As a beginner you should try make something, and just play with how to level edit, and script. See what looks nice, and what doesn't.
Don't release this map.
You can always have someone to test your map.

Later when you know how the editor works, you can start having an extra window open, with the original Amnesia maps. From there you can see how they did. You can look through the different themes (Sewer, mansion, castle) and see what looks good.