There is also a TinyMCE editor and a plain text editor. The default text editor in Moodle is the Atto editor, built specifically for Moodle. Some examples of where you will see the text editor include: Editing Section headings, description of an activity, writing an answer to a quiz question or editing the content of many blocks.
Many of these icons and functions should be familiar to anyone who uses a word processor. The Atto text editor (sometimes referred to as the 'HTML editor') has many icons to assist the user in entering content.