If Words With Friends manages to freeze up, you'll most likely have to force quit the app. To do this you will have to first view your currently running apps. On Android, you do this by tapping on the three-lined button at the bottom of the screen. On iOS, you swipe up from the bottom of the screen. From there, swipe up on Words With Friends to close it.
If your device is not responding when trying to view your running apps or simply go to the home screen, you will most likely have to restart the device.
After either of these, you should be able to open up Words With Friends where it will be reloaded and unfrozen. If the app opens back up in the same frozen position, the force quit may not have been completed successfully.