The main difference would be how we clean house. Mods have basic access to the forum and fairly limmited abilites when it comes to taking care of situations (moving threads, closing, banning, etc.). Section mods have even less control. Admins are pretty much unlimmited with most site management actions. We are able to create new forums, sections, take care of posse applications, IP bans, post news or announcements, etc. Of course, Andy, the Site Admin or Creator, has the most power but he's not here to handle the day to day. His job is keeping the place up and running. Consider him as the angry little Canadian hamster on the wheel, lol.
I guess the best way to explain the power structure would be like this (1 being the highest):
1. Admin
2. Global Mod
3. Section Mod
4. Posse Mod
Posse mods can only control things within their posse forum. They are not members of the forum staff. If you ever need any help, I would strongly advise contacting either a Global Mod or Admin as these two groups have more access and control of the site.
Hope this helps.