Installing on MacOS
A popular distribution particularly for newbies is Postgres.app. It includes generally latest version of PostgreSQL and PostGIS. Great for development and testing. Do not mix with other installations.
Homebrew users can just run “brew install postgis” and tends to be a favorite for more advanced users since there are brew scripts for most of the popular PostgreSQL extensions, not always present in other Mac distributions.
The EnterpriseDB OSX PostgreSQL combination from EnterpriseDB includes generally latest stable minor version of PostGIS.