You can’t just take a song from Internet from Spotify, iTunes, or convert a clip from youtube to mp3 etc and use it in your video as you like. YouTube’s Audio ID technology automatically scan and detect copyrighted songs inside videos.
As a video creator you don’t want to break any copyright laws.
It’s frustrating when you have been working hard on a perfect video to see YouTube take it down or add advertising on your video because of violation of the copyright.
Pond5 is a great resource online where you find high quality background tracks for your video production.
If you bought a license and intend to use the track in a production on youtube please go here: AdRev
You can read about the license agreement here:
You pay for a license, download the music in wav format together with the license and then use the tracks in your video film project.
You do not have to attribute but it’s always nice if you do, I think