This is a yellow square.
Squares have four sides. All four sides are the same length.
Square items: tables and windows.
This is a green rectangle.
Rectangles have four sides. Opposite sides are the same lengths.
Rectangle items: doors, tables, and notebook paper.
This is a blue triangle.
Triangles have three sides. The sides don't have to be the same length.
Triangle items: ice-cream cones.