Doubt In Char Drivers

Hi All, I am following LDD3 for Char Drivers. So we writing a kernel module(char driver) after that creating a char file which is representation of Character Device. So my doubt is how we will communicate with real hardware device let suppose how to communicate with our monitor . Can any one please explain how we will communicate with real hardware for read/write calls? And what is mknod is doing internally when we are creating char/block devices? Thanks in Advance