A Glass Development Kit (GDK) developer creates applications for Google Glass, a wearable technology with an optical head-mounted display. They utilize the GDK, an add-on to the Android SDK, to build immersive "glassware" that runs directly on the device. Tasks include designing user interfaces, handling voice commands, implementing touch gestures, and managing the device's camera and sensors. They ensure optimal user experience by considering the unique context of Google Glass. Developers also troubleshoot, test, and maintain their applications to improve performance and functionality, while adhering to Google’s guidelines for Glass development.