To center portions of text, you use the "center" environment.  \\'s are used
to break up lines within the environment.  Here's an example:

	\begin{center}
	This is a line of centered text.\\
	Here's another one.\\
	LaTeX is really useful.
	\end{center}

This would produce:

		      This is a line of centered text.
			    Here's another one.
			  LaTeX is really useful.

You can also center inside of other environments, by using the  \centering
declaration at the beginning of the environment:

	\begin{quotation}
	\centering
	This is a quotation\\
	whose lines\\
	are centered.
	\end{quotation}