I had no problem learning it but on the other hand I was surrounded by people knowing it when doing it, I don't think you'll have much luck figuring it out without looking at a list of shorcuts since they're essential. Unfortunatly there's not much documentation coming with it but you should be able to get all your questions answered at the ogier forum:
http://forum.starbreeze.com
Mapping for enclave is pretty much like making maps for a q3 engine game, the tech behind is very similar.
I think it only imports q1
.map files and if you'r going to make enclave maps I think it's better to spend some time learning ogier, in any case you won't have access to the textures in gtkrad.
I've tried making some simple quake maps in it and it works pretty well.