Tessellations

Check out the introductory video on tessellations.  Once you have done that, try to learn about what they are.  Read about tessellations at Math is Fun and Cool Math.

Check out these three links to create your own online tessellations:
Design a tessellation using squares.
Design a tessellation using triangles.
Tessellation creator.

Finally, you can learn about tessellations using these slideshare presentations:
Tessellations slideshare
MC Escher