I don’t use a Mac, and I don’t know what you’re referring to as Amazon Library. Ditto your Samsara folder or where it is. (Or did you mean Sansa?)
Apple wants to make it difficult for you to use anything but a doPi player, but it’s not impossible.
If you have mp3 files and a Mac you can just drag and drop them onto the Sansa.
Go to Settings/System Settings/USB Mode and put it in MSC, which makes it look like two USB drives on your computer. (One is the Clip internal memory and the other is the card slot–which obviously needs a card if you’re going to use it.
Just put the music on the Sansa. Find the mp3 file on your computer (or a folder full of them) and copy and paste it or drag and drop it onto the Sansa.
You can put files or folders into the Music folder, or you can put them almost anywhere (except Audiobooks, Podcasts or Photos, which all behave differently).
You have to make sure they are mp3 files.
First, make sure you are showing filename extension. http://support.apple.com/kb/PH10845
Sansa plays .mp3, (and .wav, .wma and .flac) .
iTunes files are .m4a . To turn those into mp3 files you can open iTunes, highlight a group of files, right-click and Create mp3 Version. Then you have to find them and transfer them over to the Clip.
Just to be extra obnoxious, Mac OSX sometimes comes up with “finder files” that point to the real mp3. They are 0kb in size and start with dot underscore, like ._01-Track1.mp3. But they’re not mp3s and don’t have any music in them to play.