https://s2editor-tutorials.readthedocs.io/en/master/
A homepage that covers almost everything you need to know about the Galaxy editor itself.
https://docs.google.com/document/d/1wvlTy-XCyCxjd4ZNuElRbqkcY5UA5pneYFl4i1LCYLs/edit
A Google word document detailing on how to make custom User Interface for Starcraft 2. Complete with custom windows and icons.