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.
As far as I know, the Linux Foundation does not provide testing infrastructure to it's developers. Instead, corporations are expected to use their massive amount of resources to test patches across a variety of cases before contributing them.
Yes, I think Kent is in the wrong here. Yes, I think Kent should find a sponsor or something to help him with testing and making his development more stable (stable in the sense of fewer changes over time, rather than stable as in reliable).
But, I kinda dislike how the Linux Foundation has a sort of... corporate centric development. It results in frictions with individual developers, as shown here.
Over all of the people Linus has chewed out over the years, I always wonder how many of them were independent developers with few resources trying to figure things out on their own. I've always considered trying to learn to contribute, but the Linux kernel is massive. Combined with the programming pieces I would have to learn, as well as the infrastructure and ecosystem (mailing list, patch system, etc), it feels like it would be really infeasible to get into without some kind of mentor or dedicated teacher.