Then you add the attacker's strength and any weapon specific modifiers to it, subtract the defender's toughness and the protection given by any armour worn. After a successfull hit, another roll is made to discover the hit location. Any armour only covers a certain location or locations, so only offers protection to that area. The armour points on that area hit are subtracted from the damage, and that total is subtracted from the wounds of the defender. Here you should use the wounds box of the right of the sheet, not the one in the profile. Most armour is has just a figure for the damage obsorbed, apart from leather armour. This generally absorbs one point of damage if the amount of damage is up to 3, but if the damage is 4 or over, then leather offers no protection.
Your wounds total is how much damage you can take before you really start to get hurt. You don't go from being fine on 1 HP to being dead on 0 HP as in DND. The lowest wounds can go is zero, but if the damage done would have made it negative the you have a critical hit. For example, one character has 3 wounds. She is hit for 5 points of damage. This take here wounds to zero, and she also sufferes a +2 critical hit. She is then hit again for another 5 points of damage, resulting in a +5 critical hit. Just shows you how useless women are at combat, really!
The result of a critical hit is rolled on a table (sorry Paul) depending on the location of the hit and the value of the critical hit. Generally a +6 critical hit will result in instant death, +5 is almost certain death, +4 is about 2/3rds death, +3 is about 50:50 death, +2 is about 1/3rd death, +1 is 1/5th death. How many fate points have you got to spare?!
After rolling for the result, I then generally read out a gory paragraph which gives a description of what happens to you/your opponents. This feature of Warhammer is unique as far as my limited experience goes, and enlivens combat up no end.