This information is in the FAQs:
These controls allow you to quickly and easily enter vBcode into your posts and messages. To use them, simply click the appropriate buttons or select items from the lists to enter vBcode.
There are three editor modes available: Basic, Standard and Enhanced mode. When using the Basic editor, there are no vBcode buttons to assist your editing. You must enter any vBcode markup manually in this editor.
When using Standard mode, highlight the text you wish to modify and press the appropriate button. This will place the proper vBcode tags around the selected text. Pressing a button while not having any selected text, will insert vBcode tags at your cursor. You may then enter your text between the tags.
When using the Enhanced mode, pressing a button will modify any highlighted text. This mode is a WYSIWYG mode, What You See Is What You Get, whereas your final post appears the same while being edited. Clicking a button while having no text selected will not have any effect.
To use the clickable smilies, simply click the smiley that you want to insert into your message, or click the Show All Smilies link (if available) to access the full list of smilies.
After I read that I did a search for WYSIWYG and the info in my post above popped up.