Question: how to transfer music from itunes library to ipod shuffle?
Answer: Launch iTunes, and then connect the iPod to your computer using the iPod's USB cable.
Click the "iPod" button at the top-right corner of the iTunes screen. ... 
Click the “Music” button, and then select the “Sync Music” checkbox.
Select “Entire Music Library” to sync all songs each time you connect the iPod to iTunes.