what's the difference between "destroy" and "delete" a user?
- destroy removes the user account and all posts by that user.
- delete removes the user account and any negatively voted posts they own.
The former is used for spammers and other types not welcome on the sites, the latter for other users who may have contributed valuable (i.e. positively scoring) content.
what's annotate a user?
This is basically adding a note to the user's account for the next moderator who comes along.
how do you convert an answer to an edit?
This is for questioners who may be unsure of how Stack Exchange works and have added extra information as an answer rather than editing the question. So on that answer you bring up the mod menu, select that option and press "Submit" and as if by magic the answer is deleted and appended to the question as an edit.