Position the center circle at the bottom of the protractor on one of the four vertices. A vertex -- the singular for vertices -- is the point which two lines converge.
Adjust the protractor so the bottom of the device is exactly in line with the bottom line of the angle you are measuring. Keep the center circle in place on the vertex at all times. Hold the protractor in place.
Look at the upper line of the angle you are measuring and see where it crosses under the upper arc of the protractor. Write down the angle degree of the specified by the protractor. Continue measuring the remaining three angles in the same manner. Remember, straight lines are angled at 180 degrees and right angles always angle at 90 degrees. Acute angles never exceed 90 degrees and obtuse angles always measure between 90 and 180 degrees.