List of shapes.
Most things in the world are made up of shapes, both 2D and 3D. Here are some of them.
An arch is a curved, self-supporting shape usually used over doorways or to support old bridges. Arches shift the downwards force at the top of the arch to a sideways force at the bottom of the arch, so there must be a strong wall holding the base of the arch up. Arches work particularly well underground where the earth holds the sideways force. When two arches are put next to each other, the sideways forces are cancelled out, so a row of arches together e.g. under a long bridge only need thin walls or pillars holding the arches up.
A cone is a shape with a round bottom that gets smaller as it goes until it reaches a point. If you cut a slice through a cone parallel to the bottom, it will be the same shape as the bottom. If you cut a slice through the cone vertically going through the top point, you will get a triangle.