Python modules are .py files with python code. Every Python file can be referenced as a module. Importing modules is similar to importing functions and is done by writing import <name of the module>. If you want to include your self written module you have to be aware that all those files have to be in the same directory.
Let`s assume that we have a self written module named whatsup.py which is in the same directory as our main file. Including it and calling functions can be done in that way:
Of course you can use the alternate import options I showed in Mastery07: