How zip codes organized America

I've always been curious about how zip codes really work and how they're managed. The fact that the entire United States can be sub-divided into these seemingly simple 5-digit (and then later an additional 4-digits) numbers is fascinating to me (I want my life to be sorted so efficiently). I know it mostly helps to sort mail rather than deliver (although I guess that's sort of the same thing), but I've never really quite understood how it works. What makes this whole system seem complicated though is the fact that the 4-digit add-on code that you often see on mail created by automated systems is dependent on the building rather than the location. As you'll see in the video above, that means that if a building gets razed and a new building is put in its place, the new building will not have the former's 4-digit code.