XF 1.2 Member/Group Permissions?

Ok, I have looked at the "Help" pages regarding this question, but I still can't figure out if I am doing this correctly. I've used vB so long, moving to a new forum software comes with a learning curve.

First off, I am having trouble figuring out how to set the permissions for all Registered Members, Admins, Etc. Is this set thru /Users/User Groups? or /Users/Group Permissions?

Then after the above is answered, what would the setting in the other be used for?

I hope that makes sense... :/