Packages extend LaTeX with new commands and environments. Load them in the preamble (before \begin{document}) with \usepackage{packagename}. Packages add features like graphics, colors, advanced math, bibliographies, code listings, and much more.

\documentclass{article}
\usepackage{amsmath}      % advanced math
\usepackage{graphicx}     % include graphics
\usepackage{xcolor}       % colors
\usepackage{hyperref}     % hyperlinks
\begin{document}
% Your content
\end{document}

Common packages:

amsmath — advanced math symbols and environments (align, gather, etc.). Often loaded first if you use anything beyond basic math.

graphicx — include images with \includegraphics. Required for figures.

xcolor — text and background colors with \textcolor and \colorbox.

hyperref — hyperlinks and PDF metadata. Load last (after most other packages) to avoid conflicts. Enables \url{...}, \href{url}{text}, and internal references.

listings — format source code with syntax highlighting and line numbers. Alternative to verbatim for displaying code.

tikz — draw diagrams, plots, and graphics programmatically. Powerful but complex; see TexLive TikZ Graphics.

geometry — customize page margins: \usepackage[margin=1in]{geometry}.

fancyhdr — custom page headers and footers. See TexLive Headers and Footers.

natbib — flexible bibliography system with author-year citations. Alternative to standard BibTeX.

Package options are passed in square brackets: \usepackage[options]{package}. Example: \usepackage[T1]{fontenc} loads T1 font encoding (better for non-English text).

Installing packages: Most common packages are included in texlive-latex-extra. If a package is missing, install via your package manager: apt install texlive-latex-extra (Debian). For newer packages or custom packages, place .sty files in the same directory as your .tex file or in ~/texmf/tex/latex/.

Finding packages: Search CTAN (Comprehensive TeX Archive Network) to find and learn packages. Read package documentation: texdoc packagename opens the .pdf manual in a viewer if installed.