This is NOT a question about which is the best framework, etc.

I have never used a mocking framework and I'm a bit puzzled by the idea. How does it know how to create the mock object? Is it done in runtime or generates a file? How do you know its behavior? And most importantly - what is the work flow of using such a framework (what is the step-by-step for creating a test).

Can anyone explain? You can choose whichever framework you like for example, just say what it is.