Watch the video below which is all about polygons. Polygons are 2D shapes with 3 or more straight sides. All quadrilaterals are polygons, but there are other types of polygons too. As you can see ...

“We trained two carrion crows to detect a distinct display among two-dimensional visual shapes ... in their place were squares, rhombi, isotrapezoids, and other various quadrilaterals.

The diagonals bisect at right angles. The sum of interior angles in a quadrilateral is 360°. This fact and the properties of quadrilaterals can be used to calculate angles.