Very carefully! ha ha!

I look up the song on yt before using. MOST ( I said MOST) times it will allow you to use it if it has that ad below the video selling the song on amazon or itunes.

I have been fooled before, that's why I say "most" times.

Other times on an old song it may not have any ads below but will allow use. Sometimes not, I have lost lots of times over the last 3 years of posting videos getting fooled. At one time I would chose a song , make the video then run a test video on yt about a minute long to save time and find out if it was allowed or not.

Sort of gambling at times.

Over the years I have reused songs since I know they will work.

There is also a site where you can look up the songs which are owned by certain labels so that you know not to use them. I forgot the site but a search on yt will produce the site. It will name bands like the Eagles that will not allow to be sued. I love the Eagles but can't use them.