How to Use a Protractor to Measure and Construct Angles
A protractor is a tool which is used by architects, mathematicians, and several other professionals. Moreover, students carry this tool in order to measure angles while learning geometry. This tool helps you in measuring or constructing any angle of a given measure. Even though this tool is quite easy to use, several people get confused about the two different scales which are drawn on the tool. You can use the following steps to either measure or construct the angles which you want with the help of a protractor.
Instructions

1
Measuring an Angle
In order to use the protractor for measuring angles, you must first find the centre hole on the protractor while it is lying flat in front of you. Observe how it is present right in the centre of the line which connects 0 degrees to the other 0 degrees. This hole is the key to measuring angles in the most accurate way possible.
Once you know where the hole is, simply drag it to the vertex or the point of the angle which you want to measure. Since the angle is drawn between two lines, you must understand that the line from 0 degrees to 0 degrees must be placed over one line while the zero must be on the vertex. On the other hand, the other line will be under a certain angle. Simply find that angle by looking at the degrees which are being shown on the scale of your protractor.
Since there are two different scales on the protractor, make sure you are using the correct one. The one which you should use must start from zero, and not 180 degrees. 
2
Constructing an Angle
First use the straight side of the protractor in order to draw a straight line. This will work as the base line for constructing an angle. Once you have drawn the line, simply find the centre hole (just like the previous step) and place it over the edge of the line.
Once again, zero degrees must be on the straight line which you have drawn. Now you can choose from the several angles which have been lined up on the protractor.
Select any angle which you want to make and make a small dot with the help of a pencil. Remove the protractor and join that dot with the edge of the line where the centre hole was placed.