What is the after-roll bonus?

I don't know what it means.

I still can't understand what it does, something about extra chance to do more damage, higher % better chance, or something like that

It's a sort of a 'critical shot'. In addition to a normal roll, a bonus can be applied. ARB shows the maximum possible bonus, ARB % shows the chance to apply the minimum bonus (1).

Im still not sure how all works. if you have 10 tanks doing 8 damage adds up to 80 damage. their after-roll damage is 10%, so 1 unit have like +1 damage to his shot, add total up to 81???? im sorry its just confusing to me

If you actually watch a battle occur some of the rolls will turn gold and be higher than a regular roll. It is basically just a chance to increase your roll randomly.