@SilentDame where I got into 40k was with this webseries: http://www.theallguardsmenparty.com/ It's the story of an RPG tabletop game (I believe Rogue Trader) played between friends and the story is told from the characters perspective. Everytime I ran into something that I didn't know I wiki'd it and from there I got a bit into the lore 😅
One thing the absolutely incredible @runningoff (love you ❤️) didn't mention is that the Necrons are clearly the best faction because they're Egyptian Space Terminators that started life as a species with hyper cancer, traded their bodies to gods to be healed, got tricked by the gods, became cursed living metal, rebelled against the gods, shattered them, turned them into their own weapons of war, fought some other gods, won the War in Heaven then took a multi million year nap because they accidentally killed everything in the universe and ever since they got out of bed they've been causing more chaos than literal Chaos gods in a quest to find a biological form worthy to ascend to. I love them :3
40k is so unbelievably over the top and extra and the lore is great. It is the literal definition of grimdark though so expect some heavy content in places. The Adeptus Mechanics and their bloody servitors are a great example...
@runningoff it was one of those Commander sets like they did with Fallout. From memory the decks were Space Marines, Chaos, Tyranids and Necrons