Core module ih _cp class?

I’ve walked through EE documentation and didn’t found how can I interact with core module class from within _cp class? I have created all needed files but seems like _cp file knows nothing about its core..

documentation says:

The Core Module file is used for outputting content via Templates and doing any processing that is required by both the Control Panel and any module tags contained in a template.

I thought that core module should be available automatically in _cp class, isn’t it? Where can I read complete reference manual about module classes structure?