You just have to connect the SD card to the card reader!
Just select all your mp3 file in the folder and copy,
Then paste it in your SD card directory!
You can also drag directly the mp3 files to the SD card!
---i got this reply, thank you.
Follow up question:
You mean, I need to connect my phone or SD card to the computer to be able to save file such as mp3? What if I got the file via bluetooth then I want this transferred to the memory of my SD card, will this be possible?