Bob,
Don't know the Matsui brand specifically but....
Hopefully it will be a simple drag and drop jobby. In other words, connect the player to your PC (you should have received a cable of some sorts, or maybe it has a USB plug built into the player which you plug into a USB port).
Once connected, go into Windows Explorer and you should see the player identified as an external hard disk drive which you can open-up in Explorer.
Then, find where you store your MP3 tracks on your hard drive, highlight the ones you want on your MP3 player, right-click, pick Copy, and then right-click Paste in the folder for your MP3 player in Explorer. The MP3 data should then copy onto your MP3 player ready to be played as you wish.