So what would happen if I connect with USB cable to USB cable from laptop to PC? Which reaction will both devices get?
With a "bare" cable (without any "controller" in between)? Absolutely none.
Possibly. A current of up to 1 amp would flow between + 5V and GND (or less), but that's about it.
That depends on what you have for an operating system and what services / programs are running on both computers. So it would be e.g. Possible to access data from other computer (assuming authorization to do so) or share its hardware.
But, as I said, that depends on the availability of appropriate programs that make that possible.
USB PC direct connection.
