Beginner: Window bug. Outer wall disappears

Hello,

When I try to push a window in a wall (as learned in the tutorial section), it doesn’t disappear. When I delete the part of the window, the outerwall gets deleted as well.

How can I prevent this from happening?
The wall is in a separated layer.

Thank you! (I’m not sure if this is the right category)

First thing you need to do is read up on how to use layers correctly.