pip is not recognized as an external or internal command / not recognized as a cmdlet, function, script file, or operable program

You need to set the path to pip in environment variables. This can be done during python installation by selecting the Add Python to PATH option.

If you have already installed but forgot to select this option, you can add the path manually:

Control Panel -> System -> Advanced system settings -> Environment variables

You will see two windows: User variables for <username> and System variables. You need the first one. Click on the variable Path -> Edit, then you will see the Variable value field. At the end, add a separator ; and append the path to the directory where pip is located (for example, C: