Use the arrow on the top of Compass and align it with one of DEF's lines. It would be easiest to align N (North) with the arrow. Then using the little tick marks, note where the other line of DEF aligns. Then use the same spot to create ABC by drawing a straight line, mark a point you want to measure off of, put that dot in the middle of the compass where the arrow of the compass rotates, put a dot by the tick you noted, then use a ruler or the edge of a rectangle compass to make a straight line.