TikZ is a powerful drawing package for creating diagrams, flowcharts, plots, and graphics programmatically. Load with \usepackage{tikz}. Drawings are created inside tikzpicture environments using commands that specify paths, shapes, and styling.

Basic drawing uses coordinates and paths. A path connects points with straight lines or curves. \draw renders lines; \fill fills shapes; \node places text.

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
 
\begin{tikzpicture}
  \draw (0,0) -- (2,0) -- (2,1) -- (0,1) -- cycle;
  \node at (1, 0.5) {Rectangle};
\end{tikzpicture}
 
\end{document}

This draws a rectangle from (0,0) to (2,1) with “Rectangle” centered inside. cycle closes the path back to the start. Coordinates are in centimeters by default.

Circles and ellipses:

\begin{tikzpicture}
  \draw (1,1) circle (0.5);           % circle at (1,1) with radius 0.5cm
  \draw (3,1) ellipse (1cm and 0.5cm); % ellipse (horizontal and vertical radii)
  \fill[blue] (5,1) circle (0.3);     % filled circle
\end{tikzpicture}

Styling uses options in square brackets: color, line width, fill, etc.

\begin{tikzpicture}
  \draw[thick, red] (0,0) -- (2,0);
  \draw[line width=2pt, blue] (0,1) -- (2,1);
  \fill[green] (1,2) circle (0.3);
  \draw[dashed] (0,3) -- (2,3);
\end{tikzpicture}

Arrows and nodes:

\begin{tikzpicture}[node distance=2cm]
  \node (A) at (0,0) {A};
  \node (B) at (2,0) {B};
  \draw[->] (A) -- (B);  % arrow from A to B
  \draw[<->] (A) to[bend left=30] (B); % curved arrow
\end{tikzpicture}

The -> makes arrowheads; <-> makes double-headed arrows. to[bend left=30] curves the line; adjust the angle to curve more or less.

Grids and axes are useful for plots:

\begin{tikzpicture}
  \draw[gray, thin] (0,0) grid (4,3);
  \draw[->] (-0.5,0) -- (4,0) node[right] {$x$};
  \draw[->] (0,-0.5) -- (0,3) node[above] {$y$};
  \draw[blue, thick] (0,0) -- (2,2) -- (4,1);
\end{tikzpicture}

The grid provides reference lines. Nodes on arrow ends label axes.

Plot functions:

\begin{tikzpicture}
  \draw[gray, thin] (0,0) grid (4,2);
  \draw[blue, thick, domain=0:4] plot (\x, {sin(\x * 180 / pi)});
\end{tikzpicture}

plot draws a function. domain=0:4 sets the x-range. Use \x for the variable; wrap expressions in {...}. Trig functions use degrees, so multiply radians by 180/pi.

Flowcharts combine rectangles and arrows:

\begin{tikzpicture}[node distance=2cm]
  \node[rectangle, draw] (start) {Start};
  \node[rectangle, draw, below of=start] (process) {Process};
  \node[diamond, draw, below of=process] (decision) {Decision};
  \draw[->] (start) -- (process);
  \draw[->] (process) -- (decision);
\end{tikzpicture}

Node shapes: rectangle, circle, ellipse, diamond. The [below of=...] option positions relative to another node.

Standalone documents compile TikZ drawings independently. Use \documentclass{standalone} instead of article:

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
  \draw (0,0) circle (1);
\end{tikzpicture}
\end{document}

This produces a PDF sized exactly to fit the drawing—no extra margins. Useful for creating graphics to include in other documents with \includegraphics.

TikZ is complex but powerful. Start with simple paths and shapes, then explore advanced features (graphs, matrix layouts, 3D projections) as needed. Read the TikZ manual for comprehensive documentation.