Hi tetafrommi,
First, you may want to choose to have the sidebar displayed so we can see connected devices:
iTunes 11: Frequently used features
http://support.apple.com/kb/HT5649
Afterwards, your device should be displayed if connected:

We'll want to click on it, and choose the Music tab at the top. Let's make sure "Sync Music" is checked:

For more information, see this resource:
iOS: Syncing your data with iTunes
http://support.apple.com/kb/HT1386
Thanks,
Matt M.