I don't remember your order but here ya go.
You can join alot of diffrent guilds you dont' have to be any class to join a guild.
All classes can cast magic
To cast magic right click choose your spell from spell menu lower right of the screen when your right click and right click back
then just hit R on the keyboard and left click
a good faq there are lots at
www.gamefaq's.com just search morrowind
Anyway hope this helps