mac help needed

I am a bit new to this and am having troubles getting music from my imac onto my clip. I have updated the firmware from the PC I have without issue, formated the clip, appear to be able to get into MSC mode, as I can see the clip on my desktop, and am able to click and drag .m4a files onto the clip into the music folder, but after unplugging, the music folder is empty.

Am I missing something basic here? Can I not play the .m4a files from albums I have ripped onto my mac? If not, is there a way to convert them to a format that would be compatible with the clip or is there something else I am doing wrong?

I apologize if this is fairly remedial, but I am still trying to figure out my mac.

Thanks!

.m4a is not supported.  Try .mp3 format.  There are programs you can use to convert.

I got it. thanks!