Are you talking about the transformations question?
You have to bisect the angle formed at the centre by lines AC and BD. Use the compass to mark arcs on two lines forming the angle, from the arcs (keeping the compass open to the same degree) draw another two arcs above the angle until you find where they intercept, draw a line fron this point to the vertex of the angle and the angle is bisected. Repeat for each of the other angles and remember to extend bisecting lines to the edges of the quadrilateral.
Hope I helped.
