Building a complex web application requires careful planning, design, and implementation. Here are some general steps you can follow to build a complex web application:
- Define the Scope: Determine the objectives and requirements of the application, including its target users, functionality, performance, and security. Identify the technologies and platforms that will be used and decide on the overall architecture of the application. 
- Design the User Interface: Create wireframes and mockups of the user interface to show the layout and flow of the application. Consider the user experience and how the application will handle user interactions, such as inputs, clicks, and gestures. 
- Develop the Back end: Implement the backend of the application, which includes the server-side logic, the database, and the APIs. Use a suitable programming language and framework, and follow best practices for security, scalability, and performance. 
- Build the Front end: Implement the frontend of the application, which includes the client-side interface, the presentation layer, and the user interactions. Use HTML, CSS, and JavaScript to create responsive and accessible web pages that integrate with the backend. 
- Test and Debug: Test the application thoroughly to ensure that it meets the requirements and works as expected. Use automated and manual testing methods to identify and fix any bugs, errors, or vulnerabilities. 
- Deploy and Maintain: Deploy the application to a suitable hosting environment, such as a cloud provider or a dedicated server. Monitor the application's performance and security, and apply updates and patches as needed. 
Building a complex web application requires a multidisciplinary team with expertise in web development, design, testing, and deployment. It also requires a solid understanding of the requirements, constraints, and tradeoffs involved in building complex software systems. To be successful, it's essential to follow industry best practices and to stay up to date with the latest trends and technologies in web development. Feel free to reach out if we can help.