how do attack numbers and troop levels factor into damage numbers ?

As I have it, loosely, attack numbers higher than the opponent's defense number is vital, troop level adds +1 per level to the attack points.

Anyone wish to elaborate?

Troop levels simply add +1 to attack and defense.

And my understanding is...

Every point of attack > opponent's defense = 2% extra damage
Every point of defense > opponents attack = 1% less damage.