[quote=@6slyboy6]
[@Blackbeard] Ummmm... the lore and the context of the Warhammer Universe. What are psykers. And techno priests. And wtf are orcs doing here XD

Who are the bad guys anyway?
[/quote]

Read the setting part of this, it's only short - http://wh40k.lexicanum.com/wiki/Warhammer_40,000 

Below that there are three broad categories being the Imperium (Man), Chaos (Demons and cults) and Xenos (Aliens) Each of those lists the basic factions set in each category. Psykers can be found in almost any race, it simply means someone with Psychic power that can range from melting faces to reading someones mind. Orks are one of the Xenos races in the Universe. They are completely different from Lord of the rings Orcs in that they are normally hugh muscle bound greenskins whom smash and rip apart everything they run into. Think of them like gangs of thugs, just ones whom can rip a human in half and traverse space. 
Techno priests are a very small sect inside the Imperium (Man) They originate from Mars. It's basically a planet built on technology, there they do all the weapon design ship building all that Jazz for the Imperium and as such there grew a Monk-like society called Techpriests. Think of them like cyborg Warrior Monks. 

The bad guys are debatable, one of the nice things about this setting is whilst there are races you could defiantly signify as evil, no one is really 'good' Even the Imperium of Man are basically just trying to conquer the universe themselves. The bad guys for all intents and purposes are anyone who isn't us. That means almost any Xenos, Orks, Eldar (Space Elves) and the like but probably above all Chaos. 

A rough crash course on Chaos would be...there is another dimension called 'the warp' which can be used for wormholes as well as to draw psychic power from. The problem is there were...things inside the warp. Namely 4 things. 4 things so powerful they could be considered Gods, Khorne, Nurgle, Slaanesh and Tzeetch are their names and throughout the 40k history they have tempted and turned man with their evil ways finally to the degree in which the Imperium of man split in half, a huge huge civil war broke out when almost half of the Imperiums millitary forces turned to chaos and started to do these dark gods bidding. Obviously as a result, the Imperium hate them, see them as evil, and seek to destroy them all. 

This is a universe that has spawned hundreds of books, games, tabletop games obviously and even a film. You wont get to grips with all of its lore as there is literally too much but it's incredibly detailed and super super cool.