iTunes for Mac: Import music and video already on your computer
Add items from your computer to your iTunes library
Do either of the following:
Drag a file or folder from the Finder to the iTunes window.
If you add a folder, all the files it contains are added to your library.
In iTunes, choose File > Add to Library, locate a file or folder, then click Open.
By default, iTunes places a copy of each audio file in the iTunes folder (Home/Music/iTunes) and leaves the original file in the current location. For information about adding an alias to the file (instead of creating a copy), see Change where your iTunes files are stored.