Let's first take a look at the definition of a parabola.
Parabola : The locus of all points in a plane such that each point on the curve is the same distance from a given point as it is from a given line.
We can use Geometer's Sketchpad to construct a parabola given a fixed point for the focus and a line (segment) for the directrix.
Click on one of the following links below to view a dynamic presentation of the parabola using GSP: