Original: Bureaucrats have extended access to Special:UserRights, enabling them to add users to the 'sysop' and 'bureaucrat' groups (but not remove them), and both add users to and remove users from the 'bot' user group.
Simplified: They have more access to Special:UserRights, letting them to add users to the 'sysop' (or use Special:MakeSysop) and 'bureaucrat' groups (but not remove them), and can add or remove users from the 'bot' user group.