it really does
right.
a few things then.
firstly, losign a combat. (i'll cover general things first, and then ork specifics after)
you lose a combat if you take more unsaved wounds than an enemy. even if you now outnumber them 15 to 1 having started at 20 to 5. even if they lost 5 times as many points as you. hell, even if you lose 3 wounds and didnt lose a model, and you slaughtered 2 of them
.
if you draw (ie. same wounds taken by both sides), neither side has lost.
once you've lost a combat, you take a leadership test. this is on the highest leadership present in the unit. for marines, this is normally the sargeant (ld 9 compared to a basic marines 8) or commander (ld 10). There are certain abilities that allow you to use your commanders leadership even if he is not present in the unit - such as Marine's Rites of Battle, or imperial guard radios.
This leadership is then modified by the amount you lost by. so if i'm a marine player, and my squad with sargeant (9 ld) has just lost a combat by 3 wounds, i'll be on 6.
You then have to roll your leadership or under on 2d6 to not break.
there are other things that can modify leadership (such as Lemartes' Death Mask giving a -1 ld to all enemies in 6 inches) or make it unmodifiable (Stubborn).
If you pass then thats fine - you've taken losses, but you stand and fight.
If you fail (ie. roll higher than your modified leadership) you've broken. At this point, both players roll a dice and add their initiative. if the broken unit gets higher than the pursuer, they escape. if not, they are run down and destroyed automatically. this is an excellent way of taking out necrons, since they dont get to roll wbb on it
If you have 2 units fighting in the same combat, and one breaks but the other does not, the enemy cannot run them down as they are already engaged, so you automatically get away without doing the i+d6 test.
Orks are slightly different. There is an additional rule called 'Fearless' - orks get this when in a mob of more than 10 models. Fearless means they cannot be broken. However, it has downsides too. At the point where you would normally be looking at leaderships, you instead just work out the modifier. if you lost the combat by 3 wounds, then you take another 3 wounds. these can be saved against as normal.
Once you are below 11 models, you'll be testing against leadership. i'm not sure what orks leaderships are these days, it used to be about 5 for a boy, 6 for a nob, and 8 for a warboss, probably all a bit higher now. so if you have taken 6 wounds, and inflicted 3 on your enemy, you'll be on -3. if you've just got a nob (ie. not a warboss), you'll therefore be needing to roll 3 or less on 2d6. It should be noted that a double-1 will ALWAYS pass, even if your at -20. The bosspole allows you to inflict a wound on your own unit, and gain a reroll.
If you still fail (and realistically, once orks are taking leadership tests, they tend to fail them), you fall back. so roll d6 and add initiative to see if you get away. if you get away, roll 2d6 (or 3d6 for bikes/jump troops) for how far you run towards your own table edge. your opponent then rolls a d6 for how far they can consolidate. note that even if they could reach you with this d6, *they are not allowed to*.
If you do not beat them on the initiative+d6 roll, then the squad is wiped out. this includes any independant characters. so yes its a risk, but otoh your less likely to lose the combat with an IC present (because they tend to be vicious bastards), and if you do your less likely to break (because of the higher leadership value).
once you are broken, you will run 2d6 (or 3d6) inches a turn towards your table edge. you can attempt to rally if you are at 50% models or above. if not, your just running. you also can't rally if theres an enemy unit within 6".
you can shoot as you run, so long as people are within range (and obviously you cant fire stuff like heavy weapons as your moving).
If you rally, you get to move 3" that turn, and can shoot - but again, you count as moving. i think they can charge, but its unlikely you'll be close enough to in most cases.
There are rules for if you are charged while fleeing, but honestly it almost never happens, and the rules are different between 40k and fantasy, so i keep getting them mixed up.
Marines are slightly different again, due to their 'And They Shall Know No Fear' rule.
This means several things - firstly, that if they break in close combat, and you catch them on the initiative roll, they simply take damage as though they were fearless, rather than being wiped out.
Secondly, if they rally after fleeing, they move their 3", and can then act normally - so they can move another 6", or shoot at full range.
Thirdly, (i think) they can rally even if they are below 50%.
Wow. wrote more than i meant to. oh well. hopefully cleared some stuff up.