The major job of 3D graphics is to simulate a 3D world and project that world into a 2D location, which is the viewport window. 3D or 2D objects that we want to render are nothing but collections of vertices. These vertices are then made into a collection of triangles to form the shape of the object sphere:
The screenshot on the left shows the vertices that were passed in, whereas the screenshot on the right shows that the vertices were used to create triangles. Each triangle forms a small piece of the surface for the final shape of the object.
