I've always sound using the construction an incredibly frustrating and difficult experience, primarily because as you suggest the actual instructions they provide are unbelievably vague. (fortunately I've no interest in major modding)
I don't know how much help it will be but there is this link to Morrowind Summit
http://www.rpgplanet.com/morrowind/m.../editorfaq.asp
which provides an overview of the editor with information gathered from other sites.
Hope this helps.
