you transfer mp3 files to your flash drive on your computer (do you know how do that?)and then stick in your USB port and then transfer it to the Jukebox. These details are covered in your UVO System User's Manual on page 2-17. Lots of USB info starts on page 2-12. The Jukebox has limited capacity, a flash drive will hold much more - I use both, holding one type of genre on my Jukebox.
Would be helpful if you could fill out your Drives info, I am presuming you have the UVO system, but there is three different audio systems on 2014 models.