How can I place my banner ads in the center of html content?

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If you can see in my profile most of the banners and text were indented from left. In want in to be in the center and put same space after each text or word. Including, having a text on the next paragraph. Sorry, I don't know much on html encoding. So, I need a step-by-step procedure. This might a great help for others who don't know how to do it themselves. It will be a great help.. thank you very much!