Here is a minimal working example on how to create such a block:

% Blocks without title in Beamer
\documentclass{beamer}

% set a theme to have nice and different blocks
\usetheme{Warsaw}

\begin{document}

\begin{frame}{Blocks without title}
% create the main block
\begin{exampleblock}{Title of the block}
\end{exampleblock}

% create a other blocks, visually separated,
% that continues the contents of the previous block
\begin{exampleblock}{}
A natural but separated continuation of the previous block.
\end{exampleblock}

\begin{block}{}
This is a standard block without title.
\end{block}

\end{document}