Ben Maughan of the wonderful Pragmatic Emacs is writing a series of articles on Org mode. It's a big subject, of course, so he's starting off easy by talking about the feature that got him started: structured notes.
He covers how to get headings and subheadings; lists; numbered lists; and checklists. It's a quick and easy introduction that's written in Org format so that you can see what it looks like. As smitty (one of the commenters) says, the nice thing about Org mode is the minimal UI. You can see that in Maughan's tutorial. There's hardly anything to know to take structured notes and yet it opens up many possibilities to other functionality that Maughan will doubtless cover in subsequent posts.
If you aren't already following Pragmatic Emacs, you should definitely add it to your feed. He covers loads of useful material.