The Text Editor has many tools that assist with entering content into your course. Many of its icons and functions should be familiar to anyone who uses a word processor. You will see the text editor when describing an activity, posting to a forum, writing an answer to a quiz question, adding feedback while grading, or editing the content.
From Moodle.org Read More about the ATTO Text editor
NOTE: Hover your mouse over each button to see what the button will do. A tool-tip will pop up with informative text.
This tool allows you to format your text easily without knowledge of HTML.