Install Google Music Manager on your computer with a your iTunes library, then run it.
https://support.google.com/googleplay/answer/1229970?hl=en
You will be able to select which folders to upload to your Google Music Library. Once uploaded, you can access it from any device or computer by using the Google Play Music app or the website.
Be advised that the upload process can take a while, depending on how much music you have. It took me about 48 hours straight to upload about 6000 songs.
Posted via Android Central App.
Please excuse any typos or autocorrect derps.