Draw the first side of the triangle, the base, by using a ruler or any other straight edge to draw a horizontal line on a sheet of paper with a pencil.
Measure a 90 degree angle from one of the ends of the base. Line up the straight edge of the protractor with the base of the triangle, making sure the midpoint of the protractor is on one end of the base line. Mark the paper at the 90 degree point as indicated on the protractor.
To measure a 90 degree angle without a protractor, use any object with a right angle, such as a book, magazine or sheet of paper. Align one edge of the object with the base of the triangle, and line up the object's corner with either end of the base line. Make a small mark with your pencil somewhere along the side of the object.
Draw the second side of the triangle, the leg, by using a ruler to extend a line from the base's endpoint to the small mark you made indicating the 90 degree angle. At this point, your triangle consists of two lines drawn at a right angle to each another.
Draw the third side of the triangle, the hypotenuse. Link the unlinked ends of your triangle's base and leg by lining up a ruler to the ends and linking them with your pencil.
Indicate that the triangle you drew is perpendicular. Mark the triangle's 90 degree angle by writing 90 degrees (or 90°) on the interior of the angle.