I firstly found the song I was going to use for my advert and took the URL to use with a MP3 converter.

I then took the URL and put it into this YouTube converter which then produced a MP3 file for me to add into the reaper software and onto my advert. However I can only use 7 seconds of the song so I will have to crop the music down.

You can see the MP3 file that has been produced.