From, well, the tail of an ox. It couldn't be any simpler. Quora probably will tell me this will collapse because it's too short, so: it's very common in Brazil's countryside. It's fat (too fat for me, not my favourite food), but healthy.
We can divide octagon into six triangles. So, the sum of the angles of each triangle is 180 degrees. For octagon, the sum of the interior angles is 1080 degrees and there are eight sides. Let us make a circle in the middle of the octagon and measure the central angle of a regular octagon. A circle is 360 degrees around.
Area of regular octagon can be found the following way. From the center of the octagon we can draw lines to each of the vertex dividing the octagon into 8 triangles. We find the area of one triangle and multiply the result by 8. The central angle is divided into 8 equal parts. Each angle would be $\frac{2 \pi}{8}$ or $\frac{\pi}{4}$ degrees.