Re: Sound is off on my Android don't known how to turn it on
Welcome to Android Central! Which phone? Are you saying that you can't hear other people on a call over the earpiece speaker, and instead have to use speakerphone? Check the status bar--is there a headphone icon, even though you don't have any plugged in? If so, the headphone jack might be faulty, or there might be some debris stuck in there.
If you don't see the headphone icon, then I would suspect either a clogged earpiece speaker opening (see if there's debris stuck in it) or a broken speaker.