Can I use my notebook without a cable as a 2 screen. If yes, how does it work?
It's not working
Most notebooks have graphics inputs, almost all of them have only outputs. If yours has an input, then a keyboard shortcut should be drawn on your keyboard, which can be used to switch the picture (to the input & back again).
What do you mean?
No, that is not possible.
So just because your notebook has an HDMI port for example does not mean that the signal can go "in both directions". Mostly you can only use monitors on the notebook, but not the screen of the notebook as a monitor (for another device).