References are stored in an external `.bib` file acting as a database.
Level 1: The Database (.bib)
LaTeX
@book{knuth,
author = "Donald Knuth",
title = "The TeXbook",
publisher = "Addison-Wesley",
year = "1984"
}Level 2: Citation
Source Code
Example OutputStatic
According to Knuth \cite{knuth}, TeX is great.
\bibliographystyle{plain}
\bibliography{refs}
According to Knuth [1], TeX is great.
References
[1] Donald Knuth. The TeXbook. Addison-Wesley, 1984.
Level 3: Advanced Styles
Using biblatex allows mostly cleaner commands:
LaTeX
\usepackage[style=apa]{biblatex}
\addbibresource{refs.bib}
\textcite{knuth} % Knuth (1984)
\parencite{knuth} % (Knuth, 1984)