You can add songs manually to your iPod shuffle (1st or 2nd generation) by dragging, or you can use Autofill to automatically fill your iPod with songs from your library or a playlist. You can also add songs manually and then use Autofill to fill any remaining space.
Autofill selects different songs each time you use it.
Note: These instructions are for iPod shuffle (1st or 2nd generation) only. See iPod shuffle (3rd generation) for more information about that device.
To add songs to your iPod shuffle:
Connect your iPod shuffle to your computer.
In iTunes, do one or both of the following:
To add songs manually, drag them from your music library or a playlist to your iPod shuffle in the list of devices.
To add songs automatically using Autofill, click Settings, select your settings, and click Autofill.
To disconnect your iPod shuffle, click the Eject 
button.
For more information about using your iPod shuffle, see the documentation that came with your device or visit the iPod website.