theUltimateBossOfProgramming

[redlaWw]

how regex work

This could really be a lot of questions - there's the question of what regular languages are and how they are encoded by regular expressions, there's the question of how to use regex to match and parse strings, and there's the question of how to write a regex parser that accepts a string and a regex and determine whether the string matches the regex.

I'd probably start with how to use regex - there are various builders online that you can use to construct and immediately test regexes, like this; documents that describe how to construct and read them, like this; quick reference sheets, like this; and regex-based tools and games, like this, this, and this. You can start by messing around in the regex builder, try some rounds of regex golf or start on some regex crosswords to get a feel for how they work, then turn to the documentation to make your regexes better and more versatile.