Itemize with a dash "-" instead of a bullet

One-at-a-time method:

\begin{itemize}
\item[--] asdasd
\item[--] dsfsdf
\end{itemize}

---

Set all first-level bullet-point to --:

At preamble, in plain-TeX

\def\labelitemi{--}

or in LaTeX

\renewcommand\labelitemi{---}

These have the same effect, but if you want all your definitions to look similar you can prefer one over the other.

---

Set the first-level bullet-point to -- only in one itemize environment:

\begin{itemize}
\renewcommand\labelitemi{--}
\item asdasd
\item dsfsdf
\end{itemize}

For reference, here's a package-wise approach using the (de-facto) list manipulation package, enumitem:

\documentclass{article}
\usepackage{enumitem}% http://ctan.org/pkg/enumitem
\begin{document}
\begin{itemize}[label={--}]
\item asdasd
\item dsfsdf
\end{itemize}
\end{document}

% before \begin{document}
\usepackage{enumerate}

% after \begin{document}
\begin{enumerate}[-]
 \item asdasd
 \item dsfdsf
\end{enumerate}

Ideally, the enumerate package is already in MiKTeX so you need not download it.