Place the vertex of the angle at the central point on the protractor, and align one of the rays with the zero tick mark.
Count up the tick marks until you reach the second ray of the angle. You have just measured how many degrees are in the angle.
Multiply this number by 1/3. This is how many degrees are in your first trisecting angle. Using a straightedge, make a ray from the vertex at this angle.
Repeat Step 3, only this time, multiply the number by 2/3 instead. Mark another ray from the vertex to this angle measurement.