Can you tell me about the background music you use in your videos?

I use Music Bed, a service that provides access to a large library of licensable music, for which I have a license. Using licensed music on YouTube avoids monetization claims and copyright strikes. I think Music Bed is the service you're referring to, though I may use a couple of others. There's a ton of music available; you could Shazam to identify a specific track. I've given the music to my editor, and we now use a variety of songs. Hopefully that makes sense.