First, you need to set it up by enabling Wi-Fi syncing from iTunes in the Info tab of your iOS device.
Originally Posted by samc
Make sure iTunes is running on your computer. Then, make sure your iOS device is plugged into a power source and WiFi on. From the settings App, go to "general" and select "iTunes Wi-Fi Sync".
Q: Would you patronize a streetwalker?
A: No, I would treat her as an equal.