It is easy to insert blocks in beamer that make your slides look more organized and easier to follow. In the following minimal working example you can see the basic usage:

% use the beamer document class
\documentclass{beamer}

% set a theme to load a block style
\usetheme{Antibes}

\begin{document}

% create a new frame
\begin{frame}

% set the frame title
\frametitle{First frame}
% create a basic block
\begin{block}{Basic block title}
Basic block contents.
\end{block}

% create an example block
\begin{exampleblock}{Example block title}
Example block contents.
\end{exampleblock}

\end{frame}

\end{document}

Compiling this code yields:

From above, we can remark that each block has its own style, which is determined by the theme set (antibes in this case) but you can select another theme or even build your own custom blocks.

The blocks are specially interesting when writing mathematical presentations, since they can be used to enclose theorems, corollaries, examples, lemmas, observations, proofs, and so on.

For example, the following code:

% Math blocks in beamer
\documentclass{beamer}
% package to build the theorem-like environments
\usepackage{amsthm}

% set a theme for cooler blocks
\usetheme{Antibes}

% set a new style for remark environments
\theoremstyle{remark}
\newtheorem*{remark}{Remark}

% let’s create a frame to illustrate how beamer works
% with theorem environments
\begin{document}

\begin{frame}
\frametitle{Mathematical content}

\begin{theorem}
One is less than two, that is, $2>1$.
\end{theorem}

\begin{proof}
This is true, since $2=1+1$ and $1$ is positive.
\end{proof}

\begin{corollary}
I don’t know if this theorem deserves a corollary
\end{corollary}

\begin{remark}
This was an easy theorem.
\end{remark}

\end{frame}

\end{document}

is a minimal example that illustrates how beamer handles theorem-like environments. The output is shown below!

For more details, I invite you to read this post: “Your guide to Beamer Blocks“.