I can also recommend the book the TS mentioned, it is very good and after reading it you will understand regular expressions. It’s fine to use a cheat sheet if you want, cause if you don’t do it regularly the knowledge can sag, but the understanding is what matters. Also depending on the context, different implementations can have slightly different syntax or modifiers to be aware of.
I lent out the book to my brother once and he somehow lost it, so I never got it back. Don’t lend out book guys.
And remember not everything can be solved using a regular expression: xkcd.com/1171/