Your volume may be muted. Use the right button on the top left side of the device to turn the sound up, or open “Settings” and tap on the “Sound and Notifications” option, and use your finger to slide the volume slider to your desired volume.
If you still don't have sound, check to make sure the speaker isn't covered and the headphones are correctly plugged in. Your headphones may be broken or your headphone jack may be loose. Contact Amazon Support if problem persists.