A Java Applets developer creates small applications or programs using Java that are embedded into web pages, providing interactive features that cannot be accomplished with HTML alone. They design, code, test, debug, and refine these mini applications to enhance user experience, often involving animations, games, or other interactive elements. Their work also involves ensuring compatibility across various web browsers and resolving any bugs or issues. They may also need to modify existing applets to improve performance or add new features. Understanding of web technologies like HTML, JavaScript, and CSS is crucial for their role.