The Granny Square
The Granny Square is a traditional crochet technique.
Even though it's been around for a long time,
crocheter's continually find new ways to update its image.
It is basically a square that is crocheted in rounds instead of rows

How to Crochet a Granny Square.
Granny Square

If you're doing Granny Squares,
you'll probably need a way to put them together.
Here's a few suggestions:

How-To's For Joining Granny Squares
No Seam Join

Plarn
Plarn is "yarn" made out of plastic grocery bags.

How to make plastic yarn
Marlo's Crochet Corner
Needlepointers.com