There are two ways to make perpendicular bisectors. One way is to make semi circles and the other way is to just measure.
1. take your compass, put the point at the end of the line segment and draw a semi-circle.
2. do the same thing to the other end of the line segment.
3. take the ruler, align it to the intersections of the 2 semi-circles and draw a line.
4. label the bisector.
the end result should look like this:
1. take your ruler and measure the line segment.
2. find the center of the line and make a mark, then draw a straight line
3. label it.
Follow this Link for a video on more how to make a perpendicular bisector.