Have you tried rebooting it?
Despite all its flashy features and its different shape, Apple's iPad is a computer just like a laptop or desktop. And, just like laptops and desktops, sometimes iPad apps freeze, and freeze the iPad along with them, requiring a restart to fix the frozen iPad.
To restart the iPad, hold down the hold and home buttons at the same time. The hold button is on the top right corner of the iPad's case. The home button is the circular button just under the screen on the center of the iPad.
Hold these buttons down until the screen flashes and goes dark.
You can then restart the iPad by holding down the Hold button until the Apple icon appears. Let go of the buttons and you'll be using your iPad again in just a few seconds.