How do i dowload music to my opal M4208GR - RCA OPAL M4001 MP3 Player

You can always reference the easyRip help file by clicking on the icon with the "?" on the Module Dock. Just navigate to the section that applies to your issue and it provides images and step-by-step instructions on how to perform any task that easyRip is capable of performing.

Manual for RCA Opal M4208GR:
http://www.voxxsupport.com/images/manuals/M4208GR/media/M4208GR_DOC_OM.pdf

This player has default setup MSC mode, seeing the player as a flash drive also called a removable disk.
MSC = Mass Storage Class
When seeing the player as a removable disk in Windows Explorer:
Drag and drop the song, with mp3 or wma format, into the Music folder on the player.
Note: some wma files may have DRM = Digital Rights Management. These files might be copied or transferred onto the player but cannot be started for playback.
Important: in MSC mode always safely remove hardware, the players' removable disk, at the bottom right corner of the task bar.

Transfers to the player can also be done with software like Windows Media Player 11, RCA easyRip or other software from music stores.
This can be done in MTP mode. MTP = Media Transfer Protocol.
How to switch to MTP mode, seeing the player as Media device:
In the players Menu go to Settings. Go to Protocol. Select MTP mode / switch from MSC mode to MTP mode.