There are multiple ways to accomplish any task in drupal. Including text formating. Here are 4 ways to center text (or any other content) starting with the simplest method.
Highlight a paragraph and click the text align center button
Select the "center" style. For titles, select the "H3 Center" style
Select "Add Content" from the Additional Content section and add word "centered" to the css class field
Go into the source view and add class="centered" to all of the tags you want to center.