iTunes does not sync all my songs

I recently decided that it would be nice to have all my songs on my Android device as well as on my iPad & iPod, and to do that I needed to have all my songs synced with iTunes on my computer. I completed the update to version 11.3.0.54 but my library was empty. I remember that the last time I went on iTunes, which was probably more than a year ago, everything was there, but it was all gone. I plugged in my iPad for the first time and started a sync; that has all the music I would want on it, so I decided I could just sync it. I did that but only about half of my songs synced and then showed up. I then did "transfer purchases" and got quite a few more songs to transfer, but I still don't have any of the songs that I got off of CDs. Does anybody know how I could transfer these? Thanks!