What do I do if while playing online I can hear people talking but they can't hear me? Or vice versa?

Be sure to check all connections between your headset, controller, console, and television are all fully plugged in. 

If that doesn't work, unplug the power cable from the back of your console, wait 30 seconds, plug the power cable back into your console and restart your console. This is known as a cold reboot, or a power cycle.