Daemons are evil spirits of Chaos that have come into our universe to destroy stuff. Depending on which god they serve (or none in particular, favouring rather to worship Chaos Undivided), they can look and play very different - Khorne, The Chaos God of blood, anger, violence and hate, has vicious fighters, who use large Swords and Axes, while Tzeentch, the Chaos God of Fate and Sorcery, has demons with constantly changing body parts, that can use the Warpfire of their master. Nurgle, the Chaos God of pestilence, stagnation and plagues, has really tough demons, which mostly look like one horned zombies, and Slaanesh, the Chaos God of excess, pleasure and debauchery, has really fast demons, which resemble barely dressed human women.