A square has four sides and is flat with length and width. A triangle has three points and is also flat with length and width. A circle is flat and round with two dimensions of diameter and circumference. A pyramid is like a triangle but three-dimensional with length, width, and height. A cube is like a square but three-dimensional with length, width, and height. A sphere is like a circle but three-dimensional with circumference, height, and width. Length is how long something is. Width is how wide something is. Height is how tall something is.