References

Internal References

If the command \label{} is placed in a numbered environment, then the command \ref{} references it by number. The same descriptive string is passed to both.

\documentclass[12pt]{article}
\usepackage{hyperref} % For clickable links
\usepackage{amsthm} % For numbered theorems
\newtheorem{theorem}{Theorem}

\begin{document}

\section{First section}\label{sec:first}

Some stuff.

\begin{theorem}\label{thm:a-theorem}
A theorem.
\end{theorem}

\section{Second section}

In Section \ref{sec:first}, some stuff was done.
Theorem \ref{thm:a-theorem} was especially interesting.

\end{document}

Equations are numbered with \begin{equation} and \end{equation} or \begin{align} and \end{align} for aligned equations. An asterisk * makes them unnumbered, such as in \begin{align*} and \end{align*}.

\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}

The equation
\begin{equation}\label{eq:einstein}
    E = m \cdot c^2
\end{equation}
is famous.

Equation \ref{eq:einstein} explains the mass defect of atomic nuclei.

\end{document}

External References

External references are in a separate BibTex file. The extension of a BibTex file is .bib. In a BibTex file, an entry is denoted by @ with its type and then its information. Anything outside this environment is a comment. Google Scholar provides the BibTex format for most references.

Book
@article{feynman2014qed,
    title={QED: The strange theory of light and matter},
    author={Feynman, Richard P},
    year={2014},
    publisher={Princeton University Press}
}
Article
@article{vaswani2017attention,
    title={Attention is all you need},
    author={Vaswani, A},
    journal={Advances in Neural Information Processing Systems},
    year={2017}
}
Miscellaneous
@misc{enyeart2024latex,
    title={Latex Tutorial},
    author={Enyeart, Dustin},
    year={2024},
    url={https://latex-tutorial.readthedocs.io/en/latest/}
}

The package biblatex is for bibliographies. If the previous code block is in the file refs.bib, then the command \addbibresource{refs.bib} includes these BibTex entries. They are cited with the command \cite{}. The bibliography is printed with \printbibliography.

\documentclass[12pt]{article}

\usepackage[backend=biber]{biblatex}
\addbibresource{refs.bib}

\begin{document}

Quantum electrodynamics is cool \cite{feynman2014qed}.

\printbibliography

\end{document}