Worldbuilder is in my opinion a very easy and simple editor. When I first started working with it I had no idea it would this "easy". Hell, my first ever released map became a featured map over at
http://www.cncden.com and now I got my own page there to showcase my maps
Basically how I started is by reading the "eighteen steps to creating a multiplayer map" + "a few extra steps for skirmish maps" from the official WorldBuilder Manual, released by EA.
Read it and then just get to it. It's hard to say how easy or difficult you'll find it. By just doing it you'll see