Welcome to this section of the site.
I decided to make a page starting small of the map editor "Mapster32" that comes with EDuke32.
Here you will find video tutorials on how to design stuff in your maps.
A tip you can press ALT+S to create a red lined sector.
You can also hold the left mouse button to lock onto something to adjust it.
Pressing the J key lets you join sectors, helpful to get rid of the red lines.
This is not the only way to make water, but a very basic way on how to do it! Njoy!!