Where to start is a tough question. I'd start at first with http://wh40k.lexicanum.com mainly because, while there is a lot of fluff and non-canon in there, it gives you a good overview of the Factions and most history of the Universe. Once you've done that, try one of the Bookseries, honestly any mentioned here is good enough, though i'd start with Ciphias Cain, Gaunt's Ghosts, the first four Horus Heresy Books and Angels of Darkness/Fallen Angels.
They all give a good view into the Universe, skimming over alot of Factions and the general Feel of "everyone is a asshole ultimately". You can really pick any of those and see where you go from there, i'd suggest Dawn of War Series, the first Game including Winter Assault and Dark Crusade, as they give also some generic Idea of how the Wars are fought and the general mindset of said fights/armies.
After that, well more Books and the Table Top await.
Nouw said:
ChupathingyX said:
Wait..............
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..................
..............what?
Aren't the Necrons souless robotic zombies, why would they ally with the Space Marines?
From what I've read, they're not all loyal to C'tan and some are actually sentient.
Actually thats not quite correct. You can play Necrons as belonging to different C'tan but they arent entirely outside their Control ultimately. At best you get a very small Warband Type which has some semblence of free will. Necrons are ultimately Slaves with little to no free will at all, some are twisted depending on which C'tan they belong to, i.e. using the Outsider for your Army, while you cant use the actual Outsider as a Unit, allows you to play your Necron army more freely due to the inherent insanity of the Outsider by itself.
Still, most Necrons are slaves to the C'tan so..at best you get maybe a handful that can really be described as having free will.