The Python package manager is called pip. You will need pip to install the PyMongo driver, but, just as with Python, there is pip for Python release 2 and also pip3 for Python 3. The pip command does not work with Python 3. If you do not have pip3 available, use the appropriate installation procedure for the operating system that will house the Python code you plan to create, which will communicate with MongoDB.
For further information, please consult the official pip documentation here: https://pip.pypa.io/en/stable/.