I loved to do this kind of stuff when i was younger. Especially this kind of OS interactions. It actually gave me a lot of experience and helped a lot in my job, where i have to find solutions out of the norm.
It's really just drag and drop. I always drop the album folder, with all mp3s and then edit all with correct meta information, album cover etc, if needed.
Edit: you have to do this, in order to add them to the itunes/music library. It actually makes copies of the mp3s in the library folder iirc.
It doesn't even look for music on the hard drive, that's why it has to be added to the music library.
It's an ad from the 70s