Does your PC see it as a 'removable drive' when connected by USB? If so you can copy tracks from your PC to this drive, just as it was a USB flash drive.
You copy mp3's and mp4's over not CD tracks of course. They will need converting first.
Have another look at the packaging as it may give some clue as to the make. My daughter's mp4 player is an Opus Pro made by Sumvision but you wouldn't know it at first glance.