Click on your iPod's name (the one you assigned during the initial setup). This will open your iPod's main "Settings" page in the center of the iTunes window, where your media library previously was.
Click on the "Music" tab. Make sure the box next to "Sync Music" is checked.
Click on the "Movies" tab. Make sure the box next to "Sync Movies" is checked.
If you have an iPod Touch, it is possible to make changes to the content on your iPod without syncing it with your computer and iTunes. However, if you're not careful you could then erase that content from the device completely the next time you do connect your iPod to your computer. All you have to do is take a few precautions to make sure that you can sync your iPod without deleting its existing content.
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