\begin{tabular}{ccc}11&12&13\\21&22&23\\31&32&33\end{tabular}
produces
\begin{tabular}{ccc}11&12&13 \\21&22&23 \\31&32&33 \end{tabular}
The bracket after the \begin{tabular}, specifies columns: c for centre aligned, l for left aligned, r for right aligned
Unfortunately BOS latex, doesn't...