On the top edge of the window you'll find a selection of tabs for your iPod, including the current summary page, applications, music, movies, TV shows, podcasts, iTunes U, photos, and info. In each of these tabs you get to decide what media from your iTunes collection gets transferred to your iPod.
For example, in the music tab, you can decide to sync your entire music library, or, just the specific playlists, artists, and genres listed in the section below. When you're happy with the selections, hit the apply button in the bottom right corner and iTunes will start moving your music over to the iPod.
Discuss: How to set up an iPod Touch--photos
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