Although I don't have your textbook, I may be able to help you use a protractor.
I remember when I got confused using one. The difficulty comes in recognising the following types of angles:
- Acute
- Obtuse
- Reflex.
Acute angles are between 0 and 90 degrees and are pointy like the end of a pencil. The edge of a box, rectangle, etc, is 90 degrees, and all acute angles are less than 90. So when you are reading your protractor you know you read off the numbers between 0 and 90 to measure your angle if it's "pointy". You place the protractor on one of the lines forming the angle and then look to see where the other line points on your protractor. The symbols < and > look like acute angles facing in different directions.
An obtuse angle is bigger than a right angle (90 degrees) but not bigger than 180 degrees, which is just a flat line. If you open up a pair of scissors as far as they'll go the blades will make an obtuse angle.
A reflex angle is more than 180 degrees and looks like it's folding back on itself. Look at a clock face. Imagine the time is 11:45, quarter to twelve. The reflex angle is measured from the hour hand between 11 and 12 all the way round to the minute hand on 9. Most protractors only have angles covering 0 to 180, so you need to use the protractor in a different way and just measure the angle by adding on 180 to whatever the protractor reads.
You can use a clock face to arrange the fingers at acute, obtuse and reflex angles. Point the minute hand to 12 and just move the hour hand. The clock face is your protractor!
EXAMPLES
1 o'clock to 2 o'clock is acute; 3 o'clock is a right angle (90 degrees)
4 o'clock to nearly 5 o'clock would be obtuse.
6 o'clock is 180 degrees, a straight line.
7 o'clock onwards, measured clockwise is reflex.