[KSever]

I'm in the before stages of installing the new 200 amp meter socket, 200 main breaker and 200 amp main panel in place of my 60 amp service. I will be also installing a 100 amp sub panel off the 200 amp main panel for the upstairs in place of the 60 amp fuse box. I understand and know most of the electrical codes for my area but don't understand the ground/neutral bonding. Why is this ground/neutral bonding used and is it only required in the main 200 amp panel or do I only do this in the main breaker right after the meter socket?

Can someone please explain this ground/neutral bonding to me?