How Attack and Defense work?

[maltz]

The manual wasn't very clear in terms of the description.
For example, if your unit's Attack is 0, 10, 20... and the opponent's defense is 0.

How much % of damage is dealt?
What if your attack is 10 and your opponent's defense is 20, 30, 40?

I actually downloaded the Russian fan manual. Good I can understand the "M" alphabet because it looks exactly like the English "M".