For example , I activate NMOS for saturation region(Source is connected to ground and Drain is connected to VDD). Current flow Drain to Source and after that I feel like there is out of electron in NMOS. But it is not correct right ? Why ? After current flow from NMOS, electrons are supplied from VDD(voltage source) or something ?
Your N-channel Mosfet is missing a load between its drain and the +12V so it is shorting the power supply making lots of heat. The power supply provides billions of electrons long as it is powered.