Lables & Cross References

1. Create label:
   \begin{equation}
\label{eq:one}
e^{2\pi i}=1
\end{equation}
   
2. Reference it:
    (\ref{eq:one}),
 page \pageref{eq:one}.
   

\documentclass{article}
 
\begin{document}
   \begin{equation}
      \label{eq:one}
      e^{2\pi i}=1
   \end{equation} 
  
  
   ...

   See Equation (\ref{eq:one}),
   page \pageref{eq:one}.
   
   \begin{center}
      Run \LaTeX twice!!!
   \end{center}

\end{document}