The basic plot is that you play as a night guard at Freddy Fazbear's Pizza. The animatronics come to life at night and seem to have some sort of malfunction or malevolent intent. You have to survive the nights by monitoring their movements through security cameras and using various tools like doors to keep them out.
Well, in the Five Nights at Freddy's game story, you're a security guard. At night, these animatronic characters which are supposed to be friendly during the day, start acting really creepy. There are Freddy Fazbear, Bonnie the Bunny, Chica the Chicken, etc. They move around the pizzeria. You're stuck in the security office and must rely on things like the cameras and doors to prevent them from getting to you. If they get too close, it's game over.
The story of Five Nights at Freddy's game revolves around a night - shift security job at a pizza place filled with animatronic animals. These animatronics are not as harmless as they seem. As the night guard, you quickly realize that they have a mind of their own at night. You sit in the office, constantly checking the cameras to track their whereabouts. The power is limited, so you can't keep the doors closed all the time. It's a battle of wits and nerves as you try to make it through each night alive.