How does Camus build tension in the passage describing Meursault's walk down the beach before he kills the Arab in The Stranger?
In the middle of The Stranger, Merusault exercises his freedom by taking a walk on the beach. He loves the sea and the sand. Granted, there are Arabs stalking him and Raymond, but they do not deter him. As precaution he takes Raymond's gun. Shortly, for reasons unknown, he will unload his pistol on one of the Arabs.
Camus builds the entire novel around this climax and turning point in Meursault's life. There are three deaths in the novel: his mother's, the Arab's, and his own. Meursault will be imprisoned for killing the Arab, but he will be judged more heavily for not crying at his mother's funeral. Together, the two deaths determine his own death sentence.
In terms of tension, Camus uses naturalistic imagery and metaphor:
“At the same instant the sweat in my eyebrows dripped down over my eyelids all at once and covered them with a warm, thick film. My eyes were blinded behind the curtain of tears and salt. All I could feel were the cymbals of sunlight crashing on my forehead and, indistinctly, the dazzling spear flying up from the knife in front of me. The scorching blade slashed at my eyelashes and stabbed at my stinging eyes. That’s when everything began to reel. The sea carried up a thick, fiery breath. It seemed to me as if the sky split open from one end to the other to rain down fire. My whole being tensed and I squeezed my hand around the revolver. The trigger gave; I felt the smooth underside of the butt; and there, in that noise, sharp and deafening at the same time, is where it all started. I shook off the sweat and sun. I knew that I had shattered the harmony of the day, the exceptional silence of a beach where I’d been happy. Then I fired four more times at the motionless body where the bullets lodged without leaving a trace. And it was like knocking four quick times on the door of unhappiness.”
Meursault does not exactly give any motives for shooting the Arab. His narration blames the heat and glaring light, both symbols of external pressure and reminders of Maman's funeral procession. One may say the shooting was self-defense: the Arab had stabbed Raymond previously and was showing his blade. Or, one may say it was premeditated murder, since Meursault knowingly took the gun and shot him multiple times. The point is, though, that the legalism does not matter to Meursault: the Arab and his blade intrude on Meursault's sense of absolute freedom.
The sun and water are symbols of life, and the Arab was blocking Meursault's enjoyment of them. As an absurdist hero exhibits absolute freedom and has no values, he may behave in any way he chooses. The Arab, Maman's funeral, his boss, and the judge are all people or events that try to limit Meursault's freedom. As such, he may ignore, sleep, shoot, or shout at them. In the end, though, the deterministic society will ultimately take away Meursault's freedom and sentence him to death for their own spiteful reasons.