The Drow are dark elves, twisted to evil in the course of worship of their demon goddess Lolth. While the surface elves lived in light and beauty in the woodlands of the world above, the Drow were forced into the depths of the Underdark, where they plot their revenge against their surface-dwelling cousins and all other lesser creatures.
Drow society is harsh and matriarchal in nature: that is, females are the dominant sex, and hold all of the major positions of power. Drow males reach eminence as skilled (but expendable) magic-users or warriors, or as favoured consorts, or able crafters. In all cases male drow will defer to females.
In Drow culture, the ultimate position of status is to serve the demon goddess Lolth, the spider-queen. As a result, clerics and the priesthood attain great eminence, and the most powerful and honoured role is that of high priestess. Naturally, in a matriarchal society, only female priests can reach high status.
Drow treat non-drow creatures with casual disdain; their slaves (called "Rothe" in their tongue) are seen as tools, not individuals. A drow gives as much thought to a rothe as she might give to a hammer, or at best a prized animal. This is not to say that rothe are mistreated without thought - it is not wise to break the hammer of your neighbour, if your neighbour is more powerful than you.
Non-drow who are /not/ slaves are still treated as beneath drow themselves, even in the face of the various pacts and treaties they have developed over the centuries. Drow are inherently proud, racist and jingoistic: often directly in conflict with evidence.
Drow society is not unified and centrally controlled - their nature is too chaotic, and their demon goddess too capricious, to work that way. Instead, great noble houses form the backbone of organisation, and these work with (and against) each other to pursue the Drow agenda of revenge against the surfacers.
Drow houses can be thought of like the noble houses of medieval Japan, or the nobility & city-states of medieval Italy. Intrigue is rife, and internecine conflict is common, but in the end these differences are usually put aside (albeit temporarily) in the face of a common foe.