The Visual Editor is one of the three editing modes on Yume Wiki, and the default mode for all editors on desktop (it is not supported on mobile). Unlike the source editor which convert special markup (wikitext) into the visual appearance seen on pages, it has you edit pages as they appear directly.
For a guide on using the Visual Editor, see Wikipedia's Help:VisualEditor page.
The usage of the editor is similar to editing using a modern word processor, where simple changes can be made using a toolbar, and more complicated changes are done using separate GUI panels.
One of the main features of Visual Editor is functionality with TemplateData. Editing templates using Visual Editor involves a GUI that pulls information directly from the <templatedata> block on the template page (or the template's documentation). Adding and updating TemplateData on template pages should be a priority when writing documentation.