This is a technique to make sure time is not wasted drawing surfaces that are never shown to the user. Rendering is performed in front to back order, so hidden surfaces are never drawn. You need to conserve memory whenever possible. Rendering WireFrame mode draws only the edges of a face. Unlit scenes render quickly but objects appear flat and lifeless.
Flat mode renders a mesh with each face completely flat.
It uses face normals. Gouraud shading uses vertex normals and then light intensities are averaged over the face. Phong shading uses vertex normals, and calculates light intensities over the face. Animation Motion attributes will allow you to translate, rotate, or scale an object. In key-framing you declare the starting and ending points of a path.