The full story
Spider-Man opens with Peter Parker as a nerdy, socially invisible high school senior in Queens. On a school field trip to a genetics laboratory, a genetically engineered "super spider" bites him, granting superhuman strength, wall-crawling, a precognitive spider-sense, and the ability to shoot organic webbing from his wrists.
Peter initially uses his powers for personal gain, entering a cage-fighting contest for prize money. When the promoter cheats him out of his winnings, Peter refuses to stop a thief robbing the promoter's office—it's not his problem. Minutes later, that same thief carjacks and fatally shoots Peter's Uncle Ben. Peter catches the killer and realizes the man he let escape is the one who murdered his uncle. This is the defining trauma: with great power comes great responsibility.
Meanwhile, Norman Osborn—CEO of Oscorp and father of Peter's best friend Harry—faces a military contract cancellation. Desperate, he tests an unstable performance-enhancing gas on himself. It works, giving him superhuman strength and speed, but it fractures his mind, creating the alter ego Green Goblin. Norman begins eliminating Oscorp's board members and anyone who threatens his company, using a weaponized glider, pumpkin bombs, and razor bats.
The Green Goblin discovers Spider-Man's identity and targets the people Peter loves. In the climax, he forces Peter to choose: save Mary Jane Watson (Peter's lifelong crush, initially dating Harry) dangling from a bridge, or save a cable car full of children. Peter saves both. New Yorkers rally to defend Spider-Man—pelting the Goblin from the bridge—establishing the city's relationship with its hero.
In the final battle, Norman unmasks himself and begs Peter for mercy while secretly directing his glider to impale Peter from behind. Peter dodges; the glider impales Norman instead. Dying, Norman asks Peter not to tell Harry the truth. At the funeral, Harry—who witnessed Spider-Man near his father's body—swears revenge, not knowing Peter is Spider-Man.
Mary Jane confesses her love to Peter, but Peter rejects her. He cannot risk the people he loves. The film ends with Peter swinging through Manhattan, embracing his role as Spider-Man and the solitude it demands.