Joomla comes with a built-in text editor: TinyMCE.
Although this is OK for many users, the need to change it to something more advanced may arise. When installed, you need to make sure that the editor is selected as the default editor.
I'll show you how to do that.
The recent upgrade of Joomla! to 1.5.12 included an update of TinyMCE.
The default settings might result in problems with image alignment and other parameters if you don't change some of them in the TinyMCE editor plugin.