I own, moderate several lists. If you create the list or forum then you are the moderator by default
But other than that you can be a long time list or orum member that can be trusted and have the same sort of vision as the owner/moderator and you may be asked to help out... I've done that with lists in the past when they get big you need maybe 2 or 3 extra people to deal with the day to day issues of the list or forum. Sometimes the moderator job is to calm thing down, but mostly it's dealing with issues like bouncing mail or problems people are having... On the lists I own I've always had a policy of never ever throwing anyone off. Tho a few might have their mail filtered for a while
forums like this are a little different to a mailing list, tho, and you have to deal with things differently... Anyway, doesn't really matter where you are.