How do I run code if there isn't a player inside a Region3?

I need to detect a player inside a Region3, and then be able to run code if there is not a player inside that area.

I don't need everything, just how to create the Region3 from a part, detect a player in there, and run code if there is no player.

I don't have much knowledge on this since it is a new topic for me, and the only information that I could find is on the forums, which are closed now.