For many Joomla sites, a what-you-see-is-what-you-get (WYSIWYG) editor called JCE Editor is installed.  JCE provides you with a word processor like interface for entering text and images.  Thought you might find this quick tutorial from OSTraining on How to Align Images with JCE in Joomla helpful.

For more info and tips on JCE, go to: joomlacontenteditor.net.