You are probably familiar with 2-dimensional Cartesian geometry by now, i.e. planar geometry. With this software, you will learn about 3-dimensional space, or solid geometry.
Real-world objects exist in 3 dimensions. For example, a cuboid, or a box, is completely described by three parameters, viz. length, breadth, and height. Corresponding to that, each point in the cartesian space has 3 coordinates - x, y, and z.
For this tutorial, the x asis is along the length of the screen, the y axis is along the height of the screen, and the z axis will be the one coming out of the computer screen!!