An HTML/HAML developer designs and manages websites using HTML (Hypertext Markup Language) and HAML (HTML Abstraction Markup Language). They construct the website structure using HTML, defining elements like headers, paragraphs, links, and images. With HAML, they can write HTML more efficiently, making the code cleaner and easier to read. They also ensure the website's responsiveness across different devices and browsers. They collaborate with designers and back-end developers to implement design features and functionality, often integrating CSS and JavaScript. Additionally, they troubleshoot and resolve issues related to website layout and performance, maintaining the overall quality of the website.