An Apex Classes developer designs, codes, and modifies Salesforce applications using Apex, Salesforce's proprietary programming language. They create robust, secure, high-quality solutions that meet business requirements and enhance the Salesforce user experience. Their tasks include developing server-side logic, implementing data storage solutions, integrating user-facing elements, and ensuring high performance and responsiveness. They also conduct unit tests, troubleshoot, and fix bugs to maintain the smooth operation of Salesforce applications. Additionally, they collaborate with other team members, stakeholders, and clients to understand needs, provide technical insight, and contribute to the overall project.