I edit books, articles, games, blogs, reports, and much more. I also create indexes for books.
I freelance from my home office treadmill desk when I can, walking slowly. The first thing I do is write. I typically have two or three projects going at the same time, so I check my editorial calendar and email. Then I use an indexing program and macros to index books or Microsoft Word and macros to edit books. At my job, I start by checking email, then I might check a game for errors by playing it, or make suggestions on a training module or report. Whatever the office needs!
Taking the time to learn how to use software and other tools, like style guides, is super important to editorial work. You've all heard of spell-checking, right? There are programs that go a lot further to speed up an editor's work and ensure that little errors don't slip by. A human eye (and often, ear) is always the best editor, though. Spell-checkers won't catch it if you use "there" when you should use "here," and even consistency checkers need individual decisions on possible errors.
Here's the first step for high school students
Read The Chicago Manual of Style and the Associated Press Stylebook. If you find yourself getting bored, you probably won't want to get into this line of work. You've just saved yourself a lot of time! But if you find you have a strong preference for style choices in one or the other, you're born to edit. If Chicago is your favorite, lean toward editing books. If you prefer AP, news is your thing.
"If you get an English degree, you'll have to be a teacher."