If the formatting controls that you see look like this...


...you'll able to do some, but not all, of what (JD) describes above. After you click on the "Go Advanced" button, though...


...you'll see the full set of controls, like this:


If you hover your mouse pointer over a control it'll tell you (briefly) what it's for. What most of those controls actually do is insert BB code tags. You can read about BB code tags in more detail here. Most of them are available either through the formatting controls or by typing the brackets and text yourself.