> we could need something like: "LOW", "MEDIUM", "HIGH"
So just make a string variable that you give these 3 values? Or use integers? I don't think you need a specific variable type for that at all. Same for yes/no.
Imagine that you have a variable called size, wich can receive "LOW", "MEDIUM" or "HIGH", but by mistake at some point you assign "HIG" for it, or even another value that you tought you could, like "HUGE". It won't work and maybe the problem will not be obvious for you when it happen.
Typescript can fix that, cause you can type this variable like this:
let size: "LOW" | "MEDIUM" | "HIGH"
this way, if you assign anything else to this variable, your project won't even run and the problem will be shown.