How do you assault a vehicle in Warhammer 40k?

Answer 1

First you hit and then need to penetrate or glance the armor part you are shooting at by rolling a D6 (or more if the weapon states) adding the weapons strength and that roll up if it is the same as the side of armor you are shooting(attacking) it is a glance, if higher a penetrate and lower it does nothing.

6 makes the vehicle explode d6 from the edge of the vehicle.
5 simply destroys it
4 Immobilizes it (cannot move)
3 The vehicle loses a weapon
2 Cannot move or shoot
1 Cannot shoot

Glancing gives an automatic -2
an AP of 1 gives +1

Answer 2

Move to engage as normal. Instead of using WS to hit use the following: automaticlly hit if it did not move, 4+ to hit if it moved up to 6" and you only hit on a 6 if it moved more then 6". Resolve damage as normal against a vehicle using the back armor value. The exception to this is walker vehicles. They do have WS so resolve as normal. You only hit the front armor against vehicles. None walker vehicles are never considered locked in combat and can move away freely.

Answer 3

If you want to shoot a vehicle you roll to hit as normal. When you hit, instead of rolling to wound you roll and add the result to the strength of the weapon. If it's equal to the vehicles armour then its a glancing hit, if its higher its a penetrating hit.

In close combat its the same but your always counted as hitting the back armour value.