The microphone on my earphones is not working

First, make sure all necessary input/output cables are properly connected and not damaged in any way. Then check the mic input and make sure there isn't any dirt blocking the opening. Barring that, check the phone you're connected to, and make sure it wasn't left on mute or low volume. If none of these actions help, then try turning your phone off and on. A quick reboot can often fix issues like this.