You can't copy content from one iPod directly to another. If you want to copy music that is on your iPad to your iPod Shuffle, you'll need to copy it from the iPad and into iTunes first. Then configure your iPod so that it syncs the desired content from your iTunes library.
For iTunes purchases, you can transfer them from your iPad to iTunes by choosing File -> Transfer purchases while the iPod is hooked up. For items imported from outside of iTunes, you'll need the help of some third party software to assist you with this task. Here is a list of a few possibilities.
Well, Right, you will need to transfer the songs from the iPad to iTunes library and then sync them over to the iPod shuffle.
For details in sync to iPod via iTunes, read this:
Hope that work for you so much.