Whether asking or answering a question, you will be typing into a textbox with a menu bar at its head. At the very right of that menu bar is a "?" icon which when clicked produces this interface:
Use the icons, the menus, or the "advanced help" to get more information.
When asking a question, you will see more information in a panel appearing to the right:
One trick I use, especially for formatting comments, is to start asking a question (follow the "Ask Question" link at the upper right of any page) so I can avail myself of these features as well as the WYSIWIG rendering of the text. I then copy the text and abandon the page without posting the question (this is important!).