The editors are there to help out on the site. They fix problems in diaries and stories, help out with formatting and can delete and move things around.
Editors cannot edit comments, only stories, diaries and polls.
The list of current editors is maintained in the [FAQ].
Editors also work with Trusted Users to police the site. They have greater powers than Trusted Users, so they can delete comments and edit diaries. Deleting a diary is a last resort option, as is deleting a comment. Offensive diaries are normally moved to The Hole. If a comment is completly offensive and solely posted in order to upset the site and anger the users, it will be deleted.
The editors are generally very lenient towards new users. They will correct mistakes and formatting errors. I wouldn't worry about getting banished to The Hole unless that's what you're trying to do.
However, once your card is marked by consistent bad behaviour the editors will be much less lenient, and more likely to delete your comments and diaries if they step over the line. You have to be a pretty big idiot for it to go that far though. Once you get to this point you may be banned and your account wiped.