So I don't know how much you know about the shell, but the way that the linux command line works is that there are a set of variables, called environment variables, which dictate so me behavior of the shell. For example, $PATH variable, refers to what directories to search through, when you try to execute a program in your shell.

The documentation you linked, wants you to create a custom shell variable, called SCALE_PATH, consisting of a folder path, which contains the compiled binaries/programs of scale you want to run.

This command: export PATH="${SCALE_PATH}/bin:$PATH"

temporarily edits your PATH variable to add that folder with the scale programs you want to run to your path, enabling you to execute them from your shell.

Explaining like you are 5:

If you have worked with programming languages, you might have come across global variables and inbuilt functions/keywords. PATH is a similar global variable for your terminal session.

Every time you open up a terminal, you load up these "global variables", and you/programs can access them (or the applications assigned to them).

So, let's say you have your application (executable) as /home/werecat/corncob/bin/corn, instead of starting it with ./home/werecat/corncob/bin/corn ..., if you have /home/werecat/corncob/bin in your PATH variable, you can just use it as corn ....

export PATH="/home/werecat/corncob/bin:$PATH"

just means:

1. PATH = /home/werecat/corncob/bin + PATH
2. persist (export) path for the duration of this session (usually until you close the terminal tab)

If you see somewhere to add it to your /home/werecat/.bashrc file, it means "all commands in .bashrc file are auto-executed every time you start a new terminal session, so if you have it there, you won't need to manually keep entering the command over and over again".

You can list these environment variables by just running:

env

Also, recommend you have a look at https://www.freecodecamp.org/news/how-to-set-an-environment-variable-in-linux/.

Hope this helps. Good luck on your Linux journey.

PATH is a shell variable that defines where stuff can be executed from without writing their absolute path.

So the export PATH command just adds the scale stuff to the path.