“Ambient” refers to “ambient light” in light source calculation. The brightness affected by the surrounding environment is caused by a small collection of light scattered by various objects. However, since the calculation is extremely difficult, the brightness is normally expressed as an approximate and constant value. Brightness for shaded areas, where the light source does not reach, is determined by this ambient light value. Setting this ambient light value to red will make the shadows turn red, or pitch black if set to OFF. Furthermore, if the light of the environment is too bright, the shadow difference (contrast) disappears from the whole screen.
“Animation” refers to data for adding motions to characters and objects. (The term “Animation” is used synonymously with “Motion”.)
“Assets” refers to the data necessary for constructing a game, such as characters, backgrounds, effects, sounds and so on. You can procure a wide variety of free and/or paid assets from Asset Store where you can directly access from Unity.