[verified on 10/20/2020 - on MacOS Catalina]
Install Xcode which can be found at the Apple App store
Install brew which is used for a lot of the compiling and installation tasks. Brew is a package manager for OSX.
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
Ai-Lyn Tang. How to Download Xcode and Install it on Your Mac. Link