How to view engine .cpp files?

Where can we view the cpp files of the engine? In my project’s Visual Studio solution, the engine header files are included and I can read them, but not the source files.

For instance, I can view the header file for the Player Controller class. But if I want to learn more about how its functions work, then I’m out of luck.

Source is on github. Info on how to get it is here Unreal Engine 4 on GitHub - Unreal Engine