How do people make songs play for specific, custom events?

I wanna make myself a quick and dirty personal music mod for a specific event, kinda like this one mod I found a bit back that gives Mecha Sonic his own music, but I have no idea where to start. How would I tell the game to only play it for a specific encounter (specifically, the big Death Egg Robot.)

From tinkering with other stuff I kinda know how to make the music itself do the stuff like looping, I just wanna know how I'd make it play in the first place, since there's a whole. Language to learn and all that.