Summarize the following:
Lay your ruler on the paper, then trace a pencil along the straight edge. This line segment will form one side of your equilateral triangle, which means that you will need to draw two more lines of exactly the same length, each reaching toward a point at a 60° angle from the first line. Make sure that you have plenty of room to draw all three sides! Slide a pencil into your compass, and make sure that it's sharp! Put the point of your compass at one end of the segment, and set the pencil point at the other. Do not adjust the point of the compass, and do not change the set "width" of the tool from the compass point to the pencil point. Swing the pencil-point of the compass in a quarter-circle up and away from the line segment. Without changing the width of the compass spread, move the point of the compass to the other end. Carefully swing the pencil-point of the compass so that the new arc crosses over the first arc that you drew. This is the apex (the "top" point) of your triangle. It should lie at the exact center of the line segment that you've drawn. You can now draw two straight lines leading to this point: one from each end of the "bottom" line segment. Use a ruler to draw two more straight line segments: the remaining sides of the triangle. Connect each end of the original line segment to the point at which the arcs cross. Make sure that the lines are straight. To finish the job, erase the arcs that you drew so that only the triangle remains!  Consider tracing this triangle onto another page. This way, you can start fresh with a clean shape. If you need a bigger or a smaller triangle, repeat the process but adjust the length of the original line segment. The longer the sides, the bigger the triangle!

Summary:
Draw a straight line. Span the segment with your compass. Trace a quarter-circle arc. Switch the compass around. Draw a second arc. Mark the point where the two arcs cross. Finish the triangle.