Observe the hole in the center on the bottom of the protractor. This is called the origin.
Align the protractor so that the vertex of the angle is just underneath the origin.
Line up one leg of the angle along the protractor's zero line on the bottom of the protractor.
Observe where the leg passes through zero. If it passes through the numbers inside the protractor, you must use that scale to measure the angle. If it passes through numbers outside, you must use the scale on the protractor to measure the angle.
Take note of where the angle's other leg lines up on the appropriate scale on the protractor. This is the measure of the angle.