What is the proper way to comment functions in Python?

The correct way to do it is to provide a docstring. That way, help(add) will also spit out your comment.

def add(self):
    """Create a new user.
    Line 2 of comment...
    And so on... 
    """

That's three double quotes to open the comment and another three double quotes to end it. You can also use any valid Python string. It doesn't need to be multiline and double quotes can be replaced by single quotes.

See: PEP 257

Use a docstring, as others have already written.

You can even go one step further and add a doctest to your docstring, making automated testing of your functions a snap.

Use docstrings.

This is the built-in suggested convention in PyCharm for describing function using docstring comments:

def test_function(p1, p2, p3):
    """
    test_function does blah blah blah.

    :param p1: describe about parameter p1
    :param p2: describe about parameter p2
    :param p3: describe about parameter p3
    :return: describe what it returns
    """ 
    pass