beamer provides \pause that provides this functionality. You can add that anywhere in the slide and it will "pause" the output there, produce an additional slide for post-pause display.
Additionally, many commands typical to LaTeX have been modified in beamer to provide a so-called overlay specification. As an example, the following list show each item only on the specified slides:
\begin{enumerate}
\item<1-> First item
\item<2> Second item
\item<3> Last item
\end{enumerate}
Here, the overlay specification is contained within < >. Slide 1 will contain only the "First item". Slide 2 will contain "First item" and "Second item". Slide 3 will contain "First item" and "Last item". This example, taken from the front page of the package documentation provides another view on overlay specifications:
\begin{frame}
\frametitle{There Is No Largest Prime Number}
\framesubtitle{The proof uses \textit{reductio ad absurdum}.}
\begin{theorem}
There is no largest prime number.
\end{theorem}
\begin{proof}
\begin{enumerate}
\item<1-| alert@1> Suppose $p$ were the largest prime number.
\item<2-> Let $q$ be the product of the first $p$ numbers.
\item<3-> Then $q+1$ is not divisible by any of them.
\item<1-> Thus $q+1$ is also prime and greater than $p$.\qedhere
\end{enumerate}
\end{proof}
\end{frame}
The display depends on the theme used. Below is the first slide of the above frame code from two different themes (left: default; right Frankfurt):
There are many slide overlay specifications possible. Review the package documentation to see the format provided with each command/environment.
