\documentclass[11pt]{article}

\usepackage{marginalia}

\begin{document}

Here is some body text.\marginalia{Here is a marginal note.} Some more
body text.\marginalia[style=\footnotesize\itshape\raggedright]{Here is another
  marginal note, set in smaller text and italics, whose position has been been
  adjusted automatically.}

Some final body text.\marginalia[pos=left, valign=b, style=\sffamily\raggedleft,
width=35mm]{This note is placed on the left side of the page, wider, in sans
  serif, ragged left, and bottom-aligned.}

\end{document}