How to add rain effects, sounds, etc

Hi all. So sorry to bother you. I have been working on a relatively small horror game for the past few months now, and have now just started trying to get some rain assets into the game, yet I have no idea how to add them. My game also spans multiple rooms, and I would only like to add the sound affects to a certain area of the map. What would be the best way to do this, and could someone link a tutorial if possible?