I heard that in golden chests, there is a chance (very small, but a chance) to get a silver box form them. Its true?

yes

what does the silver box do?

Its make you to change effect on your weapons/armor but you can chosse what effect you want ^^ it will do it for you but its not 100% chance to get like: you want LP% jacket with 20%LP or more you might get 17% ^^ but the silver box makes you chosse 1 effect for the armor/weapon you want to change on

And its one other thing allmost the same its calls brown box it does chosse self the effect its change all the effect on the armor/weapon to a random effect ^^

Can we use cash to buy silver boxes?

Unfortunately you can't.

How come there are some people with so many golden chests?

Its because the most of the ppl did have playd dbo for more then 2 years and gained the silver box from the webdepot ^^

They give tickets lvl 70 (+12 weapon / +10 armors), so it´s normal that much people want them.

I meant, how come some people have many, as in, how to get that many?

I've seen people with 20 golden chests. I've only once dropped one...