A protractor is used to?

A protractor is a tool specifically designed to measure angles. It typically has markings that allow the user to determine the degree of an angle in a two-dimensional space. When using a protractor, one places the midpoint of the tool on the vertex of the angle and aligns one side of the angle with the zero line of the protractor. The point where the other side of the angle intersects the curved edge of the protractor indicates the degree measurement of that angle.

The other options, while they refer to specific geometric tasks, do not accurately represent the primary function of a protractor. Measuring circles, scribing arcs, and forming ellipses involve different geometric tools and methods that focus on constructing or measuring shapes rather than determining degree measurements of angles, which is the sole function of a protractor.