\documentclass{letter}
\signature{Your name}
\address{Your Street \\ Your City \\ Your fCountry}  % your address
\begin{document}
\begin{letter}{Company name \\ Street\\ City\\ Country} % who your sending it to

\opening{Dear Sir or Madam:}
%text goes below here
It has come to my attention \dots
\closing{Yours Sincerely,}

% you may want to leave the below out
\ps{P.S. In case you forget.}
\encl{enclosed is the other document.}

\end{letter}
\end{document}