If the iPad appears to 'hang' and is unresponsive, then you need to reboot it. Press and hold the Power and Home buttons for a long time (could be 20 seconds - or it feels like it!) until the white Apple logo appears - trust me, it will eventually. Then the iPad will reboot - that takes a while too.
It happens occasionally, so it's no big deal unless it becomes a frequent occurence. If it does, try to note what you were doing at the time - i.e. is it associated with a particular app, for example?
You'll not lose any apps or data by rebooting, so no need to worry.
Tim