To close is to shut something or to end something. You could close a door, close your mouth, or even close a deal.
This versatile word usually means "the end" or "near." When a store is closed, you can't go in: the door is closed and locked. When people are close, they are right next to each other — or they're emotionally close to one another. In baseball, the closer is a pitcher who tries to end the game. If your flight had "a close call," it almost crashed. You can close a program on a computer, and you close your eyes when you go to sleep after reading this.