To build a bar chart with D3, you combine data binding, SVG, and D3's powerful selection and manipulation methods. You start with an array of values, which represent the heights of the bars. D3 binds this data to SVG elements using the data() method. The selectAll("rect") call targets all rectangle elements, and the enter() selection creates a new SVG <rect> for each data point that does not yet have a corresponding rectangle.

Each bar's position and size are set using SVG attributes. The x attribute positions each bar horizontally, spacing them evenly across the chart. The y attribute determines the vertical placement, calculated as the SVG container's height minus the bar's value, so taller bars appear lower on the canvas. The height attribute sets the bar's height based on the data value itself, while width is calculated so that all bars fit within the SVG's width. The fill attribute colors the bars, making them visually distinct.

This approach shows how D3's data binding seamlessly connects your JavaScript data to the SVG elements, allowing you to generate and update charts efficiently. As your data changes, D3 can update the SVG to reflect those changes, making it ideal for dynamic and interactive visualizations.