Homebrew is a command line tool for MacOS for installing open source software. If you do not already have it, install it here:
From the terminal, start by adding the repository that contains the RISC-V development tools:
brew tap riscv-software-src/riscv
Next install the tools:
brew install riscv-gnu-toolchain
This should give you the tools you need for assembly language programming. Next move on to the instructions for installing CodeGrinder.
If you have an Intel-based Mac, you may also need to run:
brew install riscv-tools