In console applications there generally is a main file where you type up what you want your program to do. In event-driven GUI programs, you have event handlers for each function (such as in Visual C# Windows Forms).

In Cocoa GUI applications, I don't see a centralized place where I can make variables and run commands. For example, I can make a new class and define all its member functions and data, but I don't have a place to actually make a new object of that class. Where do I put my "actual program"? I cannot find a file where all parts of the program are put together, I only seem to be able to define classes. A main file and function exists, but they aren't supposed to be used -- `main()` just starts up the application.

How does this work? Where do I put my program's code?