\documentclass{letter}

\signature{Your Name}
\address{Your Name \\ 123 Example Street \\ Anytown, Country}

\begin{document}

\begin{letter}{The Recipient \\ 456 Sample Avenue \\ Othertown, Country}

\opening{Dear Sir or Madam,}

Thank you for taking the time to read this letter. It uses the standard
\texttt{letter} document class: set your own address and signature in the
preamble, name the recipient in the \texttt{letter} environment, and write
the body here.

I look forward to hearing from you.

\closing{Yours faithfully,}

\end{letter}

\end{document}
