Read your homework assignment again:
Quote: The argument would be a string that is the month
You are passing in an
instead of a string.
Quote: the function should return an integer that is the number of days the month has in it
You are returning a string.
You are also not doing anything with the parameter - the returned value needs to be different depending on the value of the parameter.
The Python Tutorial — Python 3.9.1 documentation
It's not clear from the wording of your homework whether you are expected to take leap years into account, and if so, which year you are expected to use.