Can I return an app that doesn't work?

You can contact the itunes store and see if they will help, http://www.apple.com/support/itunes/contact

All App Stoe and itunes purchases are made on a no return/no refund basis.You can try contacting ITunes support: http://www.apple.com/support/itunes/contact/.

You can also post what issues you are experiencing and someone may be able to assist you in getting it working.

In general all sales are final. Contact the Apple store if you feel the App was misrepresented.

Identifying the App you are talking about might help with advice or problem solving.

First thing I would do is contact the developer of the app to see what the problem might be.