The three-dimensional coordinate system has three mutually perpendicular axes, x, y and z. Here, a point needs three coordinates to be defined completely. The coordinates of the point P is expressed as P (x,y,z). Plotting P in 3D is somewhat similar to plotting P in two dimensions, only an extra axis and its coordinate have to be kept in mind.
Consider the point P’(2,-3,4). Draw the three coordinate axes (refer to attached image), and note the positive and negative directions of all the axes. To plot the point (2,-3,4) notice that x=2, y=-3 and z=4. To help visualize the point, first locate the point (2,-3) in the xy-plane. It is represented by a cross in the attached image. The point P’(2,-3,4) will be 4 units above the cross, along the z-axis (represented by the bold circle in the image).