Downloaded an app from App Store but it never appeared on my iPod touch
Power off your device and try opening the game first after the device starts from a clean boot.

If that doesn't work, you'll have to find the app on the home screen and delete it.

Here is Apple's KB on troubleshooting apps that don't open:


http://support.apple.com/kb/TS1702


Feel free to ask a second question if you can't use that document to solve your Clash of Clans issue.