Unfortunately, there aren't a whole of resources out there yet, though Apple has an official video walkthrough, and a demo "LearnMetalCPP" project that they include with it. To help with the lack of resources out there, I'm currently working on a website called metaltutorial.com that teaches how to get started with Metal in C++ from scratch using the metal-cpp wrapper library. I walk you through the code line by line, and the pre-completed lessons are available on the website's Github page. Let me know if this is of any use. Additionally, you may be able to find help in the metal discussion section of the Computer Graphics Discord server, which it seems I am unable to link here.