You can think about the canvas as the graph paper that your p5.js sketch is drawn on. The canvas uses a two-dimensional grid with ordered pairs used to describe its space. The upper-left coordinate, or the origin, has the coordinate of (0, 0). The first entry of the ordered pair is used to describe the x-axis of the canvas or the distance of pixels from the left edge of the canvas. The second entry of the ordered pair describes the y-axis or the distance of pixels from the top edge of the canvas.
The convention of coordinates makes it easy to construct complex patterns and shapes using mathematical properties of graph systems.
Explore the interactive sketch on the right to understand the coordinate system of the p5.js canvas.