What's the point of the different drives in a car?

I have a Honda Accord and it has a D4, D3, D2, and D1. I only use D4. What is the point of the other ones?
And also when would you use neutral? Like when you're going down a huge hill?

Wewe

Your owners manual will tell you more, but you use D3 etc to help hold you back going down steep hills, especially with a trailer. Neutral would not often be used with the engine running. If your car quit driving down the road, you would shift to N to try to restart while it was rolling.

If you ever had to sit in bumper to bumper traffic (on level ground) you would appreciate "Neutral". Why slam it into park when you know you are going tbe inching forward soon? Pop it into N.
D-1 low gear, no shifts.
D-2 stays in 2nd
D-3 shifts low> 1> 2, no O.D.
D-4 w/ overdrive.