How do you use a in-game mic with Gmod?

To use an in-game mic with Garry's Mod (GMod), first ensure your microphone is properly connected to your computer and recognized by your operating system. In GMod, go to the "Options" menu, select the "Audio" tab, and ensure that your microphone is set as the input device. You can enable voice chat by pressing the default key "V" to talk, and adjust your voice settings as needed. Make sure to also check the server settings, as some servers may have voice chat disabled or require specific controls.