For a recent python install, python should be available under `python`, but you should also have the `py` utility installed - this is normally helpful in selecting from a set of versions. If neither of these resolve, the first step is probably to reinstall python

With regard to installing packages, I think the general rule is that `python -m pip` is best practice, because it assures that the python you install packages to is the same one you're planning to run them on