Okay, lets see...this might lead to a wall of text, but I love explaining these things, so bear with me :D
The objective of the game is to either score 50 victory points or as many VP as you can by the end of the game (which is 7 rounds) OR advance the "threat-dial" of the God you´re playing as all the way to the end which takes different amounts of ticks depending on who you play. How do you get any of these? I shall explain a little later.
The beauty of the game, other than the fact that you play as a friggin God of Chaos (I like that fact a lot even though I don´t have any history with the Warhammer Universe...with Chaos...that´s another thing), is that you have to work towards your goal while trying to hamper the efforts of your fellow players, preferably WITH another player only to doublecross him in the next round all while the old world down below tries to fend you off (they won´t succeed with that mwuhehehe)
So, how exactly is the game played? It is divided into 6 phases which I will explain below. Spoilertags for more convenience.
Those are the phases of the game, maybe I explained them too detailed, I don´t know but now you know how the game is played more or less.
One last thing that need to be explained: The dial itself. Not only does each and every advancement you get on the dial bring you closer to total victory, it also grants you bonusses. Some Victory points or maybe a valuable upgrade to your god? There´s one upgrade for each of your three troop-types as well as two upgrades for yourself, really really useful.
And...that´s Chaos in the old world in a nutshell more or less.