How do attack, defense and armor values function?

[Action]

Lets say I have a unit of valor two Urban Militia.

Attack 4 Defense 1 Armor 1

What exactly do these values do?

Is only one value used at a time, for example if I attack another Urban militia who is just standing there, I have a value of 4, He has a value of 1? The results dont agree with this.

Or are both values used at once, for example the attack value determines how likely a man is kill, and the defense value determines how likely he is to get killed?

What about armor? Is that just to protect against arrows?

Anyone want to clue me in it'd be appreciated.

[Kraxis]

Your last assumption is correct.
Your man attacks with 4 and defends with 1, not good when the other man is the same, lots of dead very soon.

Armour is protection from arrows, and shields protect from them too, but only if you face them.

[Vanya]

"An archer to your rear makes a Proctologist's career."
-- Vanya

[Wavesword]

In STW armour provided a *small* benefit in melee. The charge bonus is added to the attack value for a charging unit, which helps change the odds in the first few 'rounds'.

[Kraxis]

Yes it applies at contact, and now contact can last until the unit is all the way out on the other side.

Armour, when upgraded in STW gave +1 to defense and +1 to Armour, so it did add more than just a little bit, it gave as much as swordsmith just the other way.
But Armour in the F1 screen shows how strong that unit is absorbing arrows.

[Dionysus9]

The following link is to Tootee's Shogun Academy. Click on Dojo and then Chapter Three to learn about combat. Of course, it is Shogun Total War being discussed, but the principles are similar (if not identical) in MTW. Then when you are done go back to the main page and read the correction to the combat formula.
http://shogun-academy.tripod.com/main.html

That should help.

And remember, spears facing a Cav charge in Hold formation generally cancel the Cav's charge bonus (there may be limited exceptions in MTW that we don't know about yet, but I doubt it).

Basically, each side is considered an attacker/defender simultaneously and the game takes it down to a one-on-one level. Attacks are made against the opponents defense, and the opponent attacks against your defense. So if the same unit-type (valor, armour, weap) are fighting eachother, each swing of the weapon has the same chance of hitting (for either side).