Download the zip file and extract it to your home directory. Mind the place where you extract it. I recommend your home directory, but once you extract it, you shouldn't move it.
Then, run the bootstrap script:
source bootstrap.shThis will require your password to install Homebrew and some packages.
After that, I recommend you run the following command to setup some of macOS defaults:
source macos/setup.shFinally, set up git with ssh and gpp signing. Edit git/setup.sh to contain your name and email, then run:
source git/setup.shThis will generate both ssh and gpg keys, and will tell you where do you have to upload them to start using them with GitHub.