Researching and playing around.

Where are you starting? This topic is extremely deep, but I think to start you should understand how most parsers work, poke around wikipedia to understand lexical analysis, context-free grammars and check the links. Play around with python libraries like Lark https://lark-parser.readthedocs.io/en/stable/how_to_use.html#getting-started

They have some examples of writing custom parsers https://github.com/lark-parser/lark/tree/master/examples

Or pick your starting point for wikipedia rabbit holes. I'm not a hugely opinionated language person, I have the features I'm used to using and semantics I prefer but don't really get opinionated about the actual syntax of most languages.

There's LALR parsers https://en.wikipedia.org/wiki/LALR_parser

Parse trees https://en.wikipedia.org/wiki/Parse_tree

Reverse Polish Notation and Shunting-Yard for the old school stuff https://en.wikipedia.org/wiki/Reverse_Polish_notation

I guess my generation (mid-30s) people who grew up interesting in computers often went through a whole language phase. I picked it up professionally and was more interested in it as a tool, rather than a purely academic pursuit, but understanding fundamentals helps you a lot when it comes to executing on whatever project interests you.