Simple Warhammer 40.000 rules explaination

Profiles:

WH40K is based around the simple fact of usage of D6s (six-sided dice) and various charts. For this they use 'profiles' on which all ecxept Attacks(A) is based on a scale of 1-10. For this, charts are also used in different forms...
Movement I will explain later. 
Here's the profiles construction and meaning: 
WS (Weapon Skill): How good a soldier is one handling a sword, axe or power fist. Simply, a close combat weapon. 
BS (Ballistic Skill): How a skilful shot the character is. Note: Some charas are better on shooting than CC, and vice versa. 
S (Strength): How physically powerful the character is. Based loosely on how well trained the chara is as well. 
T (Toughness): How resilient the chara is against attacks. Also loosely based on how well trained the chara is. 
W (Wounds): How many unsaved attacks a character can take before being taken out (Killed or knocked out, famous charas never 'die' see) 
I (Initiative): That's how speedy the chara is on reacting towards an attack. 
A (Attacks): How many attacks the chara makes in CC. It means the number of dice rolled to hit and wound. Can be increased by different bonuses (two CC weapons, assaulting etc) 
Ld (Leadership): How good courage the soldier has, and how good it is on acting alone. Marines and Commissars have a higher Ld than Imperial Guard for example, as they are better leaders. 
Save: The armour of the trooper. Some don't even have armour! Marines have a standard value of 3+. That means you have to roll more than three on a D6. 

The Turn: 

Warhammer40K is a turnbased game (I-go-U-go). Each turn is split up into sections when you do your stuff. These are: 
Movement
Shooting
Assault

Movement: 
The movement varies between soldiers. Of course Bikes and flyers and jump pack equipped troops move faster than footsloggers. Movement is measured in inches ("). Not so important in a brief but if you want to know more, tell me! 

Weapon profiles: 

You might have noticed that the weapons have profiles as well. Here follows an explanation for them: 

Range: How far the weapon can fire. The range is also dictated by what kind of weapon it is. More of this later. Some have Range: Template, which means they're flamers, most of the time. Uses a special flamer template. Anything touched by tamplate takes a hit. 
Strength: How powerful the weapon is. A lascannon has, for example, strength 9, which is only one from the most powerful! 
Armour Piercing (AP): How good armour penetration it has. If the AP matches the armour value of a soldier, the life saving armour save is neglected. (I'll give an example later) Some weapons don't have an AP
Type: The type of weapon it is. There are 6 different types of weapons. Can have a multiple of choices. 
Pistol: Range is always 12". If stationary a soldier fires two shots, if moving, fires one. 
Rapid Fire: Range is always 24". Soldier may one fire one shot up to 12" if moving, two shots up to 12" if stationary OR one shot up till 24". 
Assault X: Range varies. X indicates the number of shots. Always fires to maximum range, even if moving. 
Heavy X: Range varies, but is from 24" to 48" mostly. Cannot be fired if moving, only fires if stationary. Exception for this rule is Terminators, Walkers and tanks. X number of shots fired, to maximum range. 
Ordnance: Super Heavy guns, only used by the Imperium, in fact. Cannot be fired if moving, and if stationary, can't fire other weapons than the Ordnance. Uses Ordnance blast marker. Anything covered by blast marker is hit. 
Blast: If a weapon has the Blast addy, it causes a blast. Any model covered by the template takes a hit. 

Here's a few examples: 

Bolt Pistol: R:12" S:4 AP:5 Pistol 
Boltgun: R:24" S:4 AP:5 Rapid Fire 
Lascannon: R:48" S:9 AP:2 Heavy 1 
Flamer: R:Template S:4 AP:5 Assault 1 
Missile Launcher (frag): R:48" S:4 AP:6 Heavy 1/Blast 
Battle Cannon: R:72" S:8 AP:3 Ordnance 
Splinter Cannon: R:24" S:4 AP:5 Assault 4 

(There are of course weapons with a healthy doze of extra rules ;)) 

I also said there would be an example of what the AP is and how it works. You know what it is, but what the frekk does it work like? Well, let's say an Imperial Guardsman gets hit by a bolt pistol shot (from the Chaos enemy, commissar's shots kill outrightly,no saves). 
The Bolt pistol has, as can be seen above, an AP of 5. The Guardsman's save is on a 5+. Now, that means that the Guard's flak armour proved worthless aganst the highly explosive bolt. The Guard is down. Now, had a Marine been hit, he would still recieve a save 
as Marines wear Power Armour and that armour grants a save of 3+. A bi-thing to be dealed with later is how does (I)/Invulnerable saves work, but I deal with it here, as I'm at it. Now, that Emperor-be-cursed Chaos Marine is at it again with his 
bolt pistol, and fires a shot at a Commissar, having a refractor field above his ordinary flak armour. The Commissar usually has a save of 5+, just like the ordinary Guardsman, but (!) the Commissar has been wise and taken a refractor field to battle. This means that 
his save is no 5+(I). In short, the Bolt, although having an AP of 5, can't negate the political officer's Invulnerable save of 5+, and the Guard player gets an opportunity to save one of the most potent CC elements of his army! 

That about covers weapons. 

Close Combat special weapons: 

Here's how the CC weapons work. There are different rules for them, but they all work similarly. 

Close Combat Weapon: Grants +1 A if used together with a Pistol class gun. No other specialities in Close Combat. (CC weapons are sword, axes, chainswords, Chainaxes and the like) 
Power Weapons: (Power Swords and axes) Grants +1 A if used together with a Pistol class gun. Negates armour saves in CC. Funny thing, and very efficient against tough opponents, like Mega Armoured Orks. 
Power Fists: (And Claws) Grants +1 A if used together with a Pistol class gun. Doubles the Strength of the user and negates armour saves in CC. However, being an unwieldy weapon, the user always strikes last. 
Force Weapons: (swords, axes and staffs) Grants +1 A if used together with a Pistol class gun. Negates armour saves and, if user passes a Ld test on 2D6 (roll lower than the Ld with the 2D6) slays opponent directly, no matter how many Wounds it has! 
Lightning Claws: Grants user +1 A ONLY if the other weapon is a Lightning Claw as well. User negates saves in CC, and may reroll failed To Wound rolls. 
Eldar Witchblade: Grants +1 A if used together with a Pistol class gun. Always wounds on a 2+ on a D6. Works against vehicles in a fancy manor. Take the user S, multiply it with 3 and add the score of a D6 and Voilá! The Armour Penetration against vehicles! 

Psychic Powers: 

With the psychics it's usually stated when you can use them. If not, it's probably in the shooting phase. 
They are used in the simple manor of that if you want to use a power, you'll have to pass a Ld test on 2D6 (roll lower). If you succeed, and the opponent hasn't got any stuff to undo it with, it harms the enemy, or gives you other benefits. 
Here is where Psychic Hoods need an explanation. They're simple to use. You roll 2D6, a Ld test on your psyker, and see if you can nullify the opponents psychics. 
The most powerful psychics, should be noted, are the Tyranid Hive Tyrants, in fact! 
If one rolls a snake eyes or double 6s, the psyker is attacked by Warp Deamons and receives a S:D6 hit, no armour saves allowed, as a Deamon has tried to eat his brain! 

Special Armour stuff: 

You might have noticed that some Saves has an (I) with it. That is here that I give the explanation to that and more: 

Some soldiers, usually heroes, have "double" saves. Terminators, for example: 2+/5+(I). That means that the ordinary save is on 2+, the best there can be! But! There are weapons with AP:2 and some with AP:1, even. That means that Save:2+ means nada! That is were the Termie can use his 5+ Invulnerable save. It's not as good, but it's a chance to survive, isn't it? 
So, (I) means Invulnerable. And that means that one can take those saves instead of an ordinary, when the ordinary is neglected. As a matter of fact, the Invulnerable rule overrides the rules for Power Weapons and their relatives. 
Some charas ONLY have an Invulnerable save. This might sound good, but it seldom proves so great. There's a big gaming difference between 4+ and 3+. An Assassin (With 4+(I) save) won't have the same life span against an Eldar Falcon with Shuriken Cannon as a Terminator Captain, with a save that looks like this: 2+/5+(I). See my point? 

Vehicles: 

Vehicles comes in different classes, and as they're not so important for the story, I'll just lightly touch the subject: 

Classes: 

Normal: Moves up to 12". Usually Tanks with tracks and all. Doesn't assault
Fast: Moves all the way up to 24". Mostly skimmer (hover-craft). Doesn't assault
Walkers: Moves up till 6" normally and 6" in the Assault phase to get into close combat. 

The class also dictates how many weapons they can fire while on the move. Not so important here. 

The Vehicles also have a special profile: 

Fast and Normal: Front Armour:X Side Armour:X Rear Armour:X BS:X 
Walkers: WS:X BS:X S:X I:X A:X Front Armour:X Side Armour:X Rear Armour:X 
(X is exchangeable for the values) 

Here are two examples: 

Leman Russ Battle Tank: Front Armour:14 Side Armour:12 Rear Armour:10 BS:3 
Space Marine Dreadnought (walker): WS:4 BS:4 S:6(10) I:4 A:2 Front Armour:12 Side Armour:12 Rear Armour:10 

Now you may have noted the so-called Armour values. These are used when seeing if weapons penetrate the hard shell of a tank. 
They exist on a scale from 9 to 14. Here's how they are used: 
Example: A Space Marine armed with a Las Cannon fires at a Chaos Space Marine Predator. He's lucky, and hits the renegade tank in the side. The Predator-class tank has an Armour Value of 11 on the side. Here comes the 'fun' part. That means, when you laugh manically as you roll the D6 that will invitably seal the fate of your opponents Predator! Now, the Marine player rolls a 4 and adds that to his Las Cannon S of 9, which totals 13. A penetrating hit! The Predator is most surely toast! Now, had he rolled a 2, it would've been a glancing hit. A 1 (called fumble) would just have left a funny shaped dent in the side armour of the Predator. 
In short: If a vehicle is hit, roll D6. Score equal to AV is a Glancing Hit, score greater than AV is a Penetrating hit. There are charts for the various hits, which are consulted when knowing what kind of hit it is. Roll a D6 on these charts. Needless to say, a 4+ on the Penetrating Hit chart means the vehicle is destroyed. However, a 4 on the Glancing Hits chart means that the vehicle is immobilised. 

There are more to vehicles, but only if you want to know, I'll put it here.