Hi, welcome to Android Forums, I'm sorry it's taken so long to get to your question.
There are a couple of ways you can do this. First, if you have a microSD card that came with your phone (if not you could purchase one). Attach your microSD card to your computer then drag and drop the music you would like.
Also, you could attach your Samsung Galaxy Discover to your computer as a mass media device. This will work fine as well.