Why isn't changing the material of an object visibly working? First off, I'm putting it out there that I'm pretty new to Blender. The problem is that when I select any object, or faces of a mesh, and attempt to change the material, it doesn't visibly change. A video is linked below so what I'm trying to explain can be seen in further detail.

https://youtu.be/RdlvJl-wcfQ

If you have a solution, please leave it below.
Thanks.
Because you're not in LookDev or Rendered mode (https://docs.blender.org/manual/en/latest/editors/3dview/controls/shading.html). 

As a side note, maybe you should start out with a basic tutorial, before you hop into your own projects. It may seem discouraging to actually having to learn something before one can produce results, but so is pretty much every skill that is not trivial.