electromechanical counter; can I get help on understanding how the mosfet/flyback diode interact?

https://www.youtube.com/watch?v=nU86qobWoYM I want to emulate this circuit, but I am afraid of shorting my arduino by wiring it incorrectly.

Simple Electronics

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A Neat Mechanical Counter!

In this video I take a fun look at a mechanical counter that was sent to me by a good friend; Another Maker. I go as far as tearing it down and taking it even further! Make sure you subscribe to Another Maker: https://www.youtube.com/c/AnotherMaker Thanks for watching! If you feel like supporting the channel please consider supporting on Pat...