I was just perusing that link, and my god you have just saved me so much frustration. The shortcut:

⌘+` Switch between document Windows in current application

Solves the single most confusing thing I have dealt with on OS X! By happenstance of populations, almost none of the Mac-owners I interact with are power users of any sort (programmer, accountant, etc.). When using their keyboards and fumbling around like an idiot, I always ask "How do I go to the other window of Chrome?" or similar, and they don't know what I mean. I have Googled for this before, but could never figure out how to phrase the action to get an answer.

If I could reduce my karma just to be able to increase yours more than one for this comment, I would. Thank you very much.