Connect the MP3 player to your computer with a USB cable
Wait for the device to appear in File Explorer or Finder
Open the MP3 player storage folder
Open the folder on your computer that contains your music files
Select the music files you want to add
Drag and drop the files into the MP3 player folder
Wait for the transfer to finish
Eject the MP3 player safely from your computer
Disconnect the USB cable
Check the music library on the MP3 player
Repeat the transfer if needed