Jumping ahead to the video on LLVM, the instructor mentions his prior LLVM tutorial/intro which looks really helpful as an overview, with more informative links. Probably the best get-started tutorial I've come across yet:
The kaleidoscope tutorial for LLVM is a good intro tutorial to read before one gets deeper into LLVM. The tutorial is in c++ but you can follow along in any language with LLVM bindings: https://llvm.org/docs/tutorial/
https://www.cs.cornell.edu/~asampson/blog/llvm.html
This is a great resource, I've wanted to learn how to use LLVM to compile to RISCV assembly for a while, e.g.
https://llvm.org/docs/RISCVUsage.html