That's my go-to these days, but sometimes I like to see a diagram from this one: https://regexper.com

I've just slowly learnt it by experimenting with it over the past few years. People have mostly mentioned matching, but I use it more for string manipulation.

I'm still not as intermediate a programmer as I'd like to be, so it's great when I need to invert a design decision for example. A similar code structure in multiple places, maybe across multiple files. It also means I don't miss anything, like I would if I did it manually.

Second this: https://regex101.com/

Super intuitive and great definitions / descriptions of everything.