Solution:

We can identify shapes by counting how many sides and corners there are. In the first picture, the ruler has 3 sides and 3 corners, so it looks like a triangle. In the second picture, the handkerchief has 4 sides and 4 corners, so it looks like a quadrilateral. In the third picture, the gift box has 6 sides and 6 corners, so it looks like a hexagon. In the last picture, the toy has 5 sides and 5 corners, so it looks like a pentagon.