How does reading app like Wattpad and Scribd work?

I am still new to web development environment. I would like to know how does wattpad work? How does wattpad post user's story/article on their website? As example, I write a story about 'Pinocchio'. I publish it on my account. The data about my story(pinocchio) will be sent to Wattpad database. Does my story will be written in html form (Pinocchio.html)? So, when other people read my story, does the wattpad database sent it in Pinocchio.html form? Just want to know.