Have you look at this page, I think that you have not select any music.
Setting up syncing
Before setting up syncing, download and install the latest version of iTunes. Wi-Fi syncing requires iTunes 10.5 or later and iOS 5 or later. You can change your sync options at any time. Each time you sync, content is synced between your iOS device and computer to reflect new, updated, or deleted content. If the iOS device does not appear in the Devices section or if you are unable to sync, please see this article for troubleshooting.