\documentclass[12pt,a4paper]{article}

\newtheorem{thm}{Theorem}
\newtheorem{lem}{Lemma}
\newtheorem{ex}{Example}
\newtheorem{rem}{Remark}
\newtheorem{cor}{Corollary}



\title{Title of the  Paper}

\author{First Author, 
\thanks{Address of First Author.  \protect\url{mailto: Email of First Author} ,
\protect\url{https://orcid.org/}}
\and  Second Author
\thanks{Address of Second Author.  \protect\url{mailto: Email of Second Author} ,
\protect\url{http://orcid.org/}}
%\and   Third Author
%\thanks{Address of Third Author.  \protect\url{mailto: Email of Third Author} ,
%\protect\url{https://orcid.org/}}
}

\date{\today}



\usepackage{amsmath,amssymb,eulervm,doi}



%\crefname{equation}{}{}
%\let\eqref\cref

% if using bibtex for the bibliography
\usepackage[square,sort,comma,numbers]{natbib}
\bibliographystyle{abbrvnat}


\renewcommand{\vec}[1]{\text{\boldmath$#1$}}


\begin{document}

\maketitle

\begin{abstract} Write here:
what you have done and why it is important. \\
\emph{2020 MSC codes:} 0000; 
\emph{keywords:} style, format, typesetting.
\end{abstract}

\section{Introduction}
The text of the paper starts here. Citation \cite{Henderson} can be included in the text.


\section{Title of Section 2}
\begin{thm} Statement of the theorem.
\end{thm}


\section{Conclusion}
A brief summary of the work and future directions for this research.


\paragraph{Acknowledgements}

\bibliography{bibexample}

%If you don't use BiBTeX then before \end{document},  please use the commands 
 %\begin{thebbliography}(11)
 %\end{thebibliography}


\end{document}