I have 12v poser supply for electronic lock. It has 3 valuable pins: +12V, GND and PUSH. So, when I want to unlock the lock, i need to push PUSH pin to GND. How can I push 12v line to ground with Arduino Nano?
A definite answer isn't possible without more information about the lock. You likely want something like this:
Drive IOPIN HIGH to ground the PUSH pin.
Many other parts could be used in place of the IRLML2502. It's convenient for driving directly from an IO pin. Whether you need the flyback diode D1 depends on the lock.