In the next part of this setup you will be asked to run the psql command. This is a tool that is shipped with Postgres that allows you to communicate with Postgres through commandline. In order to setup commandline properly to know the  psql command you must setup the PATH environment properly!

The best way to setup your commandline to work with postgres in commandline is to follow the steps mentioned on Postgres App's documentation portal:

https://postgresapp.com/documentation/cli-tools.html

This documentation talks about adding postgres to your PATH variable, now this sounds like a strange foreign language, believe me I know! In essence if you think of commandline like a piece of software that strictly talks by text interface, then the commands themselves are "instructions" now the commandline needs to know what instructions it can have available.

By default MAC ships with common "instructions" like "cd" (change directory), "ls" (list files), etc.

Postgres installed with a bunch of "instructions" now we just need to tell your MAC commandline where to find them. That's what the PATH variable is for! It tells your MAC where to find instructions for other software.