I am trying to get an app for my iPad and I am getting an unknown error message

Without more information it's hard to help. You might want to start here:

Using itunes on iPad: http://support.apple.com/kb/HT1491

iTunes troubleshooting: http://www.apple.com/support/itunes/troubleshooting/

Try this - Reset the iPad by holding down on the Sleep and Home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons. (This is equivalent to rebooting your computer.)

 Cheers, Tom 😉