How to find the common factors of 2 numbers
Indentation &amp; style
One of the most distinctive features of Python is its use of indentation to mark blocks of code. Your code is not properly indented (each level of indentation should be equivalent to 4 spaces not like this:
def print_factors(x,y):
 l = []

like this:
def print_factors(x,y):
    l = []

Check pep8 https://www.python.org/dev/peps/pep-0008/ the official Python style guide, you'll find it helpful when learning the basics of Python code style and naming conventions.
Return
a function should not print anything, it should return
print (list(set(l).intersection(m)))
#len(print (list(set(l).intersection(m))))

and print is a function in Python 3.x, so it's very obvious it has no length
len(the commented line).
len
len() is used to get the length of sequences:
my_list = [1, 2, 3, 4]
print(len(my_list))

output: 4
Docstrings
Python documentation strings (or docstrings) provide a convenient way of associating documentation with Python modules, functions, classes, and methods. An object's docsting is defined by including a string constant as the first statement in the object's definition.
it is generally a good practice to use docstrings in your functions explaining what the function does that are usually enclosed within triple quotes:
def print_factors(number1, number2):
    &quot;&quot;&quot;Return factors of number1 and number2.&quot;&quot;&quot;
    # do things
    # return something

Descriptive variable names
l = []
for i in range(1, x + 1):
    if x % i == 0:
        l.append(i)
m = []
for i in range(1, y + 1):
    if y % i == 0:
        m.append(i)
print (list(set(l).intersection(m)))

what is l, what is i what is x ... names should be descriptive to improve the readability of your code (whether people that are reading your code and trying to understand or you reading your own code in the future) and here's an example:
factors_1 = []
factors_2 = []
for divisor in range(1, number1):
    if number1 % divisor == 0:
        factors1.append(divisor)
for divisor in range(1, number2):
if number2 % divisor == 0:
    factors2.append(divisor)

The code

Your function is not even doing what it should be doing (returning
the number of common factors not the factors themselves.
You don't have to iterate over the whole range of the number, you iterate up to the square root of the number is sufficient to find all factors.

This is how the code might look like:
def get_factors(number):
    &quot;&quot;&quot;Generate factors of number.&quot;&quot;&quot;
    yield 1
    for divisor in range(2, int(number ** 0.5) + 1):
        if number % divisor == 0:
            if number // divisor != divisor:
                yield divisor
                yield number // divisor
            if number // divisor == divisor:
                yield divisor


if __name__ == '__main__':
    number1 = int(input('Enter first number: '))
    number2 = int(input('Enter second number: '))
    number_1_factors = set(get_factors(number1))
    print(f'Factors of {number1}: {number_1_factors}')
    number_2_factors = set(get_factors(number2))
    print(f'Factors of {number2}: {number_2_factors}')
    common_factors = number_1_factors &amp; number_2_factors
    print(f'Number of common factors of {number1} and {number2}: {len(common_factors)} factors.')