Peter Parker was just a 15 year-old orphan taken in by his aunt and uncle when he was suddenly bitten by a radioactive spider during a school field trip. Because of the bite, he acquires strange abilities that lead him to becoming New York's new vigilante known as "Spider-Man"!
The Green Goblin is Norman Osborn, a wealthy CEO of a company known as Oscorp. He adopts his villain identity with becoming boss of the city's organized crime in mind, and decides that defeating Spider-Man will set this position in place. He is Spider-Man's archnemesis.
Gwen Stacy is Peter's first true love. They met as undergraduates at Empire State University and eventually started dating. Unfortunately, Gwen's father is caught in the crossfire of one of Spider-Man's fights with Doctor Octopus, and Gwen, unaware of Peter's alter ego, blames her boyfriend for it. This causes a rift between them, but she still deeply loved Peter, so their romance continued. Later on, she is killed by Green Goblin, who knew Peter loved her.
Doctor Octopus is Otto Octavius, a former atomic-research consultant. He created four robotic arms to assist him in his work, but an experiment gone wrong grafts the arms to his back and grants him telepathic control over his new appendages. The accident affects the scientist's mind as well, resulting in his mental instability and criminal acts. He takes on the name Doctor Octopus as he tries to dominate crime in New York, much like the Green Goblin.