A hexagon is a flat shape, all in one plane, with six sides all of equal length. Each of the six angles measures 120 degrees, so the total interior angles of a hexagon measure 720 degrees (120 multiplied by 6). The hexagon can be cut into six equilateral triangles, all the same size.
The perimeter of a hexagon is the sum of the lengths of all the sides. All the sides are the same length, so that's the same as the length of one side multiplied by six.
The area of a hexagon is the same as the areas of all six equilateral triangles added together (or one equilateral triangle multiplied by six).
One place that hexagons occur in nature is in water ice: the molecules of water (two hydrogen atoms and one oxygen atom) always freeze together in the shape of hexagons.
Bibliography and further reading about geometry: