Originally Posted by Peckish

It's an option that you change in your settings. Go to User CP (user control panel), you should see a menu list on the left. Scroll down to Edit Options. On that page, scroll down to the very bottom, there is a box titled Miscellaneous Options. In the Message Editor Interface, there's an option for "Basic Editor, a simple text box" or "Enhanced Interface - Full CKEditor Editing". You want the Enhanced Interface option. Click "Save changes" at the very bottom and you will be good to go.