At any publishing business, one of the most important people on the production side is the copy editor. Magazines and newspapers, especially, could not get along without the eagle eyes of an editor, even in this age of spell check, grammar check and writing check. They do proofread material, but they may also offer suggestions for editing content.
A good copy editor will probably have a degree in English or journalism. Whatever his degree is in, he will have strong writing skills, but more importantly, good editing skills as well. Good editing involves being able to reword a passage so that it sounds better, but does not destroy the writer's "voice." Good editors also have strong grammar skills. Reporters without journalism or English degrees can make serious grammatical errors, and the copy editor has to be on the alert to catch these before they make it into print.
A publication, particularly a newspaper, lives and dies on its perceived accuracy. If people start noticing many grammatical errors and poorly worded sentences, they will start to wonder whether the publication can get its facts straight if it can't even catch an error in apostrophe usage. When these doubts creep in, circulation can start to drop.
At most publications, the copy editor is the last set of eyes on a story. The writer composes the story and, hopefully, does preliminary editing and runs spell check. The writer's editor then reads the story, making changes here and there, but is usually more concerned with content than with mechanics. When the copy editor gets the story, she is concerned with both.
Everyone has seen stories in newspapers and magazines that had paragraphs repeated or some other glaring error. A vigilant copy editor could have prevented those errors from ever making it to the press. This is why it is important for the person to print out a physical copy of the page, rather than reading it on the computer all the time. A hard copy of the page allows the editor to see the whole article, rather than just pieces at a time.
The copy editor checks the story carefully for spelling errors, formatting errors and content errors. He will check to see that local place names are spelled correctly and look for a hundred other things. Most also write headlines on stories, so they have to think of appropriate, accurate headers for articles.
This person is also responsible for putting the stories on the page and for page design in many cases. He checks to see that the articles get on the page in their entirety and that, if they continue on another page, they do indeed "jump" to that page. Deleted paragraphs at the ends of columns and missing jumps give copy editors the nervous fidgets.
A good copy editor also checks any doubtful-looking facts. He checks numbers in stories to make certain they are correct and ensures that the correct pictures run with the proper captions, with all people in the picture correctly identified. In short, it is this person's job to make sure that every page, every article, story, brief, word and headline is correct. Since the responsibility for errors always falls on his head, it's a tough job. However, when it is done well, the company has a publication of which to be proud.