How do I know to do that? Most projects just say "Install OpenCV" or, if you're lucky, give you the step-by-step for doing a pip install. Assuming you already have pip.

I remember the first time I sat down to really do something with python, step 1 was setup a virtual environment...

I never got to step 2 that week

>How do I know to do that?

The answer, unfortunately, is: you don't - at least not from the docs of all libraries you are trying to use. Maybe from some.

I found it by googling - so shared it, since it might help you.

A less than perfect system, I know.

Yes, I remember that installing pip itself was slightly tricky or involved, a while ago. I think they have made it simpler in recent versions, and it also comes pre-installed with some Python versions, likely 3.x and recent versions of 2.x.