The Little Book of Rust Macros is a pretty good, but dense, overview of how macro_rules! can be used. (Procedural macros are a completely different beast).
https://github.com/rust-lang/rust/search?q=macro_rules&type=
Looking at some of those and reading https://doc.rust-lang.org/rust-by-example/macros/syntax.html and https://doc.rust-lang.org/reference/macros-by-example.html can potentially be instructive.