1. Cubemaps define the way light reflecs, if I'm not way off. Essentially, they make your map look better. Read
this.
2. light = A light which emits light from it's center.
dynamic light = lights which can be pointed, moved around, turned on and off and so on. In general, lights that have physics.
light_environment = Acts as a sun, beaming down light from the skybox.
Also, please post in the correct forum.