A coordinate system refers to two number lines that intersect at right angles. The figure below shows the coordinate system.
Notice how the horizontal line or blue line is called x-axis and the vertical line or red line is called y-axis.
Because the x-axis and the y-axis lie on a plane, we can also call the coordinate system a coordinate plane.
The main purpose of a coordinate system is to locate points. Once you know how to locate points, you could also use the coordinate plane to graph lines, quadratic equations, and so forth ...