I’m confused – Add Music to Video‎‎‏‏‎ ‎ Review

So I made a video and I wanted to add Mine by Bazzi over it to make one of those “Send this to your crush” videos and so I bought mine on ITunes and everytime I added the music, when I merged the music and my video together literally nothing happened and it was the same video as before. Now I’m giving it 3 stars because I don’t know if I did something wrong but it’s very confusing and there is not tutorial or anything.
Review by I'm a cat so deal with that on Add Music to Video‎‎‏‏‎ ‎.