A D3.js tutorial demonstrates fundamental DOM manipulation by building a smiley face with animated eyebrows. The example shows an SVG face whose eyebrows move dynamically, illustrating how D3 selects and modifies elements. The code uses `d3.select`, `append`, and `attr` to construct the face from SVG circles and paths, then applies transitions to adjust eyebrow positions. It relies on D3 v5, rendering everything as SVG within a 960x500 viewport, with accompanying CSS for styling and layout. The dataset is implicit—the face geometry is hardcoded rather than loaded from external data.