Hello,
To answer your question, rather than a wall of text, here are two comprehensive guides to the two steps you need, preparing the SD card followed by locating your itunes library and transferring the files.
SD card prep:
http://www.wikihow.com/Format-an-SD-Card
Transferring your iTunes library:
http://support.apple.com/kb/HT1751
The limiting factor in transferring and accessing the files will be:
1. The capacity of the SD card; iTunes files downloaded from the apple store tend to be very high quality, pushing the file size higher.
2. If the files were purchased from the iTunes store, others may not be able to access the files without logging into your iTunes account due to the DRM (Digital Rights Management)