So this game has me curious but I know nothing at all about the Warhammer universe or the Dawn of War storyline so can I just jump into this and understand what's going on?   
 
I'll try to read som Wiki stuff but what's the most important things to know?

Go to the Lexicanum wiki and read the basic lore of all the races at least. Also go Ork, their dialog is awesome.

" Go to the Lexicanum wiki and read the basic lore of all the races at least. Also go Ork, their dialog is awesome. "

" @Venatio:  If you're literally just starting out in DoW2, I'd suggest playing as the Space Marines first. Not only are they the strongest units overall, but their expensiveness will teach you the value of keeping your units' health in mind. Once you have them down, feel free to switch to another race and start playing around with the shitty AI until you find one that suits you. Also, I've got a guide in progress here on GB for DoW2:R if you want to check it out. As for the lore, I can give you the short version:  In DoW2, the Blood Ravens recruiting worlds are under attack from a Tyrannid invasion along with the Orks who hate everything and the Eldar who are mostly just being dicks for some reason I can't remember. After a long campaign they manage to develop a poison and shoot it into the Hive Fleet after destroying the Hive Tyrant, halting the Tyrannid invasion. Then in Chaos Rising, you discover that Eliphas (from DoW1 Dark Crusade if you care) was brought back to life through an almost literal deus ex machina, and the forces of Chaos have decided to creep across your world and corrupt or kill everything in your path. On top of that, you know that there is a traitor somewhere in your group (canonically, it is your Force Commander, but in the game it depends who has the most corruption near the end). You just barely manage to hold the Chaos invasion back and slaughter Ulkair, the avatar of the Chaos plague god Nurgle in a battle that takes a whole fucking hour and a lot of cheesing to beat (one thing I'm glad they didn't bring back).  Now in Retribution, the Imperium has decided that the Blood Ravens just aren't worth it anymore, and now they are going to launch an exterminatus that will wipe out every living thing in the sector. However, Blood Ravens Captain Gabriel Angelos has asked Inquisitor Adrastia to investigate Kyras, the Chapter Master of the Blood Ravens and root out his corruption in order to stop the Imperium before they arrive and turn every planet in the sub-sector into a sheet of glass. "