Above is an image showing the conventional orientation of 3D x, y and z axes in a Cartesian coordiante system. Note that there are other ways to draw this same orientation which could be equally correct; the orientation of the axes as a whole is arbitrary, but the axes relative to each other should always be "right-handed" as shown. For instance, you can also imagine x and y axes pointing horizontally and vertically respectively, with the z axis coming out of the 'page'.
