A developer is primarily involved in creating and maintaining web applications. They are skilled in various web technologies such as HTML, CSS, JavaScript, and server-side languages such as Node.js. They also work with databases, understanding how to read and write data. Their responsibilities include designing user interactions on websites, developing servers and databases for website functionality, and coding for mobile platforms. They ensure optimal performance of the applications and troubleshoot issues. They also work collaboratively with other team members, like UI/UX designers and testers, to deliver a seamless user experience. They adhere to best practices in web development and maintain up-to-date knowledge of new technologies.