You can use the Code editor to edit HTML directly. The Code editor displays exactly what WordPress saves to the database.
You can use this editor if you know HTML. But be careful when using the Code editor: one missing character can mess up your whole page!
Plus, the built in Code editor is not a very good HTML editor. There’s no syntax coloring, matching of opening and closing tags, nor any of the other basic features that makes editing HTML directly a little easier.
Stick to the Visual editor unless you are trying to fix a formatting problem that you can’t fix in the Visual Editor and you’re comfortable editing HTML directly.