How it install ipa files to ipod?

First off, cydia (the actual app) is installed on the ipod after a jailbreak, so you cannot sync such an app to your ipod if it isn't jailbroken. Second, cydia is ONLY installed on jailbreak devices, its not an app that you can drag and drop by itunes. Try jailbreaking it actually with some kind of recent jailbreak software for your ipod on a specific firmware and then cydia will be installed directly onto the device.