After the initial cinematic, you'll find yourself near a small, abandoned shack. Your PDA will activate, marking a general direction towards a 'Rookie Camp'. Follow the faint path, being mindful of small 'Whirligig' anomalies that can disorient you. These are easily avoided by walking around their visible distortion fields. You might also encounter a few 'Blind Dogs'; a single headshot with your starting pistol should suffice.
As you approach the camp, you'll hear distant gunfire and shouts. This indicates the presence of other stalkers and potential danger. Approach cautiously, using cover. The camp is usually located near a cluster of ruined buildings, identifiable by the flickering campfires and the presence of other NPCs. Once inside, speak to the desated quest giver, typically marked with an exclamation point on your mini-map, to advance the story.