Open your CMD as administrator and type PATH (prints the output of your system PATH Variable). There have to be a PATH directing to your Python Installation directory. Only with that system Path your cmd knows where python.exe is and search there for python.
Normally the Python Installation Setup asks if you want to set a Python Environment PATH Variable. Maybe run the setup again and watch out for that option. And I think there was a checkbox to automatic install pip for python.
If you want to set the Path Environment Variable use this:
https://superuser.com/questions/949560/how-do-i-set-system-environment-variables-in-windows-10
If you want to manually install pip with GET-PIP you have to download get-pip.py first and then run it with python.
Download get-pip from here.
https://pip.pypa.io/en/stable/installing/#installing-with-get-pip-py