Step 1) Place the non-pencil part of the compass at point W and the pencil part at point X. Draw a circle. This circle has a radius of WX.
Step 2) Keep the compass the same width, place the non-pencil part at point X and the pencil part at point W. Draw a circle. This circle has the same radius.
Step 3) The two circles intersect at two other points, A and B. One point is above WX and the other is below. Connecting AB forms the perpendicular bisector.
See the diagram below.
