A mod (or moderator) takes care of everything chat related. He mutes, warns, etc. On some servers mods also have permissions to ban, Guildcraft has admins for this. A helper is almost the same as a mod, but is more focussed on helping (as the name says, obviously).
- The Mod rank mainly consists in managing the chat and answering questions. - The Helper rank is practically the same as the Mod rank when it comes to the permissions you have. This rank is for people who like to help other people by answering their questions on the forum and in game.
There is actually no difference, as said before, since you can help other people just as much when you're a mod as when you're a helper. Its more just a progression towards admin stage. Also the helper rank on the forums is not given due to a certain bug which disallows them from editing or deleting their own posts. -Shadoe