Theory:

Step 1: Draw a line segment \(PA\).
 
output-onlinepngtools (27).png

Step 2: Place the protractor on the line segment \(PA\) and the mid point of the protractor at point \(P\), as shown in the figure.
 
output-onlinepngtools (30).png
 
Step 3: On \(PA\) from the right side of protractor start counting from \(0°\) in the ascending order (counter-clockwise direction) and finally mark a point \(Q\) using a sharp pencil at the point \(90°\) on the semicircular edge of the protractor.
 
output-onlinepngtools (36).png
 
Step 4: Remove the protractor and join \(PQ\).
 
output-onlinepngtools (6).png
 
We get the required angle \(∠APQ\) \(=\) \(90°\).