Every intersection of sides creates a vertex, and that vertex has an interior and exterior angle.
For the definition of angles and parts of circles, you can consult previous articles.
So, in general, this means that each time we add a side, we add another 180° to the total, as nicely states.
Exterior angles are created by extending one side of the regular polygon past the shape, and then measuring in degrees from that extended line back to the next side of the polygon.
All the vertices, sides and angles of the polygon lie on the same plane.
You can measure interior angles and exterior angles.
The interior angles of a trapezoid always measure 360°.
The answer is that angles are formed inside a circle with radii, chords, and tangents.