Regular expressions have always been something that have mystified developers, even those seasoned ones looking to match the most complicated data. If you're just venturing into the world of regex, PHPMaster.com has a good guide to help you wade through some of the basics.

It makes all the sense of ancient Egyptian hieroglyphics to you, although those little pictures at least look like they have meaning. But this… this looks like gibberish. What does it mean? [...] When you’re looking to go beyond straight text matches, like finding "stud" in "Mustard" (which would fail btw), and you need a way to "explain" what you’re looking for because each instance may be different, you’ve come to need Regular Expressions, affectionately called regex.

The include a (somewhat) complicated example regex string and break it down chunk by chunk - groupings, character sets, multiple matching, delimiters and more (the pattern matches valid email addresses). They show how to use it in PHP with preg_match, preg_replace and preg_match_all for different situations.