This task has two parts, and each part has a question in it, to answer here in comments. It introduces GeoGebra - a dynamic geometry + algebra software, and the communities using it. 

Part 1

Download GeoGebra and play around freely for a while, trying different things. You can draw objects, like points and lines, and make designs. You can move your objects around. You can also make objects stay put! For example, if you add a new point exactly at the intersection of two lines, however you move the lines, the point stays attached to that intersection.

If you need help, these sites have additional tutorials:

http://mathandmultimedia.com/geogebra/

http://notropis.net/geogebra/VideoTutorials.html

Make a square using GeoGebra. Now drag lines and points that form your square. Does the shape stay square? Make a square that stays exactly square (maybe changing in size or rotating) however you drag its points and lines around. If you are an advanced GeoGebra user or want to play harder, feel free to expand on this task by constructing other objects.

Question about Part 1

Find three ideas about geometry that students can learn if they make an exact square in GeoGebra, like you did. It can be something students will have to notice themselves, or something you will be able to point out for them once they had that experience. 

Part 2

Put your square construction into GeoGebraTube, the community collection of materials. Include the link to your construction in your response to this task. While there, check out other people's materials!

Question about Part 2

Find a GeoGebra applet that models something and that you think students would like. What does the applet model? What would students learn about the properties of what is modeled if they built such an applet?