>>11975824
You can download this
https://www.retromags.com/files/file/7069-official-duke-nukem-3d-level-design-handbook-the/
You need to download comic book reading app to read it
It's an old book made in the 90's so some of the hotkeys are wrong compared to mapster32 but I only found one so far, the panning/scaling texture hotkey is different (the hotkeys are listed in the editor anyway). Most of the text of the book covers all the special effects, so for now just read up to how to create sectors, and texture stuff, and place sprites, which is pretty intuitive desu, aside from remembering not to move with WASD.
There's also this guide
https://infosuite.duke4.net/
I think when you download eduke32 it comes with tutorial.map which shows off every possible special effect