How to get music from USB to iTunes on Macbook Air

I saw a similar question to this that was answered clearly, though mine is a bit different. So I put my USB in, have iTunes open and I went up to file and did add new playlist and chose the file from my USB that had my music. So I did all this and even though you say it make take awhile my iTunes or Mac aren't showing any signs of the music coming onto my iTunes.

How do I know if the music is coming onto my iTunes and how long should this take?