Hi Marcus!
These are all common issues when working with JavaScript build tools for the first time.
First we need to make sure Node and NPM are actually installed properly.
What happens runs “npm -v” in the command line?
Once we make sure that is working properly, running npm install should work properly in the downloaded example plugin for the course. This plugin does get installed directly into WordPress like any other plugin and you will want a local copy of WordPress running to follow along.
Lets get these two steps running and go from there with your other questions. You can find some work around to not using build tools, but it will be best if you take the time to learn a bit now as most real Gutenberg development is going to require some sort of build process.
Hope that helps, let me know how these first steps go.