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.
Method 1
Highlight a paragraph and click the text align center button
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Method 2
Select the "center" style. For titles, select the "H3 Center" style
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Method 3
Select "Add Content" from the Additional Content section and add word "centered" to the css class field
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Method 4
Go into the source view and add class="centered" to all of the tags you want to center.
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Complexity
Intermediate