Bureaucrats are senior editors, they've contributed to the wikia heavily, or are the founder of the wiki. Along with being full fledged administrators, they have the ability to promote regular users to staff.
Administrators are able to ban, block, protect pages, delete pages, and so much more. They can promote users to chat moderator, but can't promote users to any other staff position.
Chat moderators are trusted users who moderate the chat. They are able to kick and ban users from chat, and that's really it.
Content moderators are able to delete and protect pages, images and much more.
Rollbacks are able to undo edits on pages with the rollback button.