You can try this to get it out of Recovery Mode:
Unplug the device from the USB cable if it's connected. Then hold down the sleep/wake button until it turns off. Let go of the button and then hold it down again until the Apple logo reappears. Let it go and the device may boot up.
This only works, of course, if your device was working properly previously. Otherwise, or if that doesn't get it back to normal operation, you'll need to to try to restore it: