Open up an angle with the slider and see how the protractor marks read it. Then in the quiz, read an angle from the protractor marks alone.
The first time you use a protractor, it's confusing which set of marks to read. The rule is actually simple: line up the angle's vertex with the protractor's center point, line up one side with the 0 mark, and read off the mark the other side points to — that's the angle.
Angles get different names depending on their size. Greater than 0° and less than 90° is acute, exactly 90° is a right angle, greater than 90° and less than 180° is obtuse, and exactly 180° is a straight angle. Acute and obtuse are ranges, but right and straight angles are only that name at their exact value — 89° is still acute, and 91° is already obtuse. Open up the angle with the slider and see for yourself how the protractor marks read it.