Visual editor is the secondary way of editing articles. It gives less precise control over the article, but it is more beginner-friendly.
To use the editor, press the pencil icon in the upper right corner of the editor and pick it from the list. The icon might not always be there - that is because some namespaces don't have it enabled (if your page link has a colon
: in it, it probably uses a namespace).
You might have been redirected to this page from the revision history view. If an edit has "Tag: Visual edit" next to it, it means it was done with the visual editor. This is important because the editor can corrupt certain wiki text features which were there but aren't supported by the editor.