Your iOS device is like any other computing device, occasionally it is good practice to shut it down and reboot it. This clears everything out and gives your device a fresh start.
To shut down your iOS device, whether an iPad, iPod touch, or an iPhone, hold down the power switch on the upper right-hand corner, then follow the directions. To restart (you may want to wait a bit — 10-30 seconds — after shutting down before powering up again), hold down the power button until the device reboots.