Well, if you haven't had the opportunity to get a grounding in regex before, then you don't have to feel bad about not knowing it.
But since regex is pretty cool, and there's a lot of cool stuff you can do with it, I encourage you to take a look at the following tutorial -- it's the one that taught me everything I know:
http://www.regular-expressions.info/
One of the most valuable things it does

is provide detailed step-by-step explanations about what the regex engine sees while it works.