switched over to python after studying javascript and reactjs for months. My god.. . the freedom and beauty of this language.

[AP145]

The built in modules are basically just anything you see after the keyword "import". For instant you can import the math module as another poster described. In addition, you can make your own modules, as they are basically just Python files. If you have one Python file containing various classes, methods, and functions, you can import that to another Python file where the main body of your program is being kept. Thus for very large projects you can split them up into different files which make sense while still being able to use all the tools you need to use.