Corners are everywhere. Two perpendicular lines form a corner. Rooms and streets have corners too. If a child misbehaves in class, the teacher might make him stand in the corner.
The key to a corner is that it leads in two directions: when you look at the corner of a room, you could hang a picture to the right or left of the corner, but not in the corner itself. A street corner usually has a street sign and sometimes a bus stop, too. A square table has four corners, but a round table doesn't have any corner. Notice how when you look straight at a corner, there's nowhere to go? That's why corner is also a verb. If you say, "I cornered him," it means you trapped him and gave him nowhere to turn. Whenever we don't see a lot of options, we feel cornered.