Raiders operate as groups of bandits that prey on those who are out on the open road in the Wastelands. Occasionally, a large and well-equipped group of Raiders will go after a Stronghold if it has something that they want.
Raiders have shunned all that was the Old World and have adopted a new philosophy of life: If you can kill it, it's yours. Raiders have become little more than tribal groups rallying around a powerful leader who maintains his / her authority by providing access to food / fuel and ammo to his followers. This is often accomplished by targeting those outposts and travelers that can't defend themselves against a pack of angry, hungry savages that would just as soon kill you as look at you.
Some Raiding groups look for slaves that they can sell or use. Others look for material wealth like fuel, food and ammo but others have devolved to such a state that they look at their targets out there on the Wastes as a source of food.