How to write properly an accent in a web address?

You can use the UTF-8 (hex.) representation:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{hyperref}

\begin{document}

\href{http://www.something.com/cami\%C3\%B3n/ }{link}

\end{document}

A site with a table to look up characters: http://www.utf8-chartable.de/

As Heiko Oberdiek mentions in his comment, the browser might help to get the correct encoded URL: you can copy&paste from the address bar or use the "Copy Link Address" facility.