1. Turn your device off, wait a few seconds and then turn it back on. Now check for sound.
2. Make sure the mute switch n the left side of the device is in the up position. Check for sound.
3. Make sure the volume level is set to a high volume level.
4. Attach your earphones and try to listen for sound. Do this several times.
5. Make sure there is nothing covering the speaker or clogging the speaker.
If after those things, you still don't have sound, connect it to your computer, backup your data, music and photos, and then restore it via iTunes. Afterwards, do not restore from a backup. Check for sound. If the sound still does not work, assume they are toast and make arrangements to get them fixed via local repair shop or do it yourself.