(Sorry, there was no way to do a preview file for this without giving away the whole thing for free.)
Since Teachers Pay Teachers does not support .gsp files, the file is a .gsp file that can be extracted from a (supported) .zip file.
This file allows you to graph parametric equations in Geometer's Sketchpad. You can animate the creation of the graph to demonstrate the idea, and there is a "printer-friendly" option if you just need the graph.
The file has an Instructions tab with specific instructions on how to use the file.