First paragraph, no alignment attribte. This page demonstrates the use of paragraph and heading elements in HTML. It also shows the 'address', 'blockquote' and 'pre' elements that are other paragraph level elements.
Second paragraph, should be centred.
Third paragraph, is right aligned.
Blockquote is used for formatting a quotation.
Pre. Preformatted code, not pretty but useful for code listings asusually appears in fixed-width font.