Numerous web sites and videos stand ready to show you how to construct a bisector. It is far easier to get help from one of those than here.
The basic idea is that you set your compass to have a distance somewhat greater than half the distance between the points you want to bisect. (Setting it to approximately their distance apart works pretty well.) Then you make arcs on either side of the line between the points.
Use the same compass setting to make arcs from both the points you want to bisect. The arcs should be drawn so they have points of intersection. The line between those intersection points is the bisector of the segment (and figure) between the given points.
That process of drawing the arcs and using a straightedge to connect their points of intersection constitutes the construction you are asked to do.
In (3), the point S is where your bisector crosses the given curve.
In (4), the two bisectors of AB and BC will be expected to cross each other at approximately the midpoint between A and C.