The book by Moritz Lenz is quite good. https://link.springer.com/book/10.1007/978-1-4842-6109-5

There's also this polished three-hour introductory lecture: https://www.youtube.com/watch?v=eb-j1rxs7sc

Combine that with reading up on details in the reference and you're in for a decent start. https://docs.raku.org/reference