How to cite a reference on Beamer as (author, year)

I would recommend using biber (the default) instead of bibtex as the back end for using biblatex. With the standard author-year style, there are two main citation commands:

• \textcite{} produces Author yyyy
• \parencite{} produces (Author yyyy)

To get the comma between the name and the year, you need:

• \renewcommand*{\nameyeardelim}{\addcomma\addspace}

So here's a complete example of what you want:

\documentclass{beamer}
\begin{filecontents}{\jobname.bib}
@book{Saussure1995,
    Author = {Ferdinand de Saussure},
    Publisher = {Payot},
    Title = {Cours de Linguistique G{\'e}n{\'e}rale},
    Year = {1995}}
\end{filecontents}
\usetheme{Madrid}
\usepackage[style=authoryear]{biblatex}
\renewcommand*{\nameyeardelim}{\addcomma\addspace}

\addbibresource{\jobname.bib}
\begin{document}
\begin{frame}
\frametitle{A frame title}
\begin{itemize}
\item Langue et parole \parencite{Saussure1995}
\end{itemize}
\end{frame}

\end{document}

For printing the bibliography, you should typically use [allowframebreaks] on the frame that contains the \printbibliography command.

I think this can solve the problem. Just add the \bibliographystyle{apalike} before the \bibliography{}. I used it on beamer and works fine.

\begin{frame}
    \frametitle{Referências}
    \bibliographystyle{apalike}
    \bibliography{bibliografia.bib}
\end{frame}