One easy granny square crochet pattern and detailed instructions can be found on About.com. A large collection of additional granny square patterns can be found at AllCrafts.net.
A granny square is a crochet pattern that forms the basis for a number of different projects. Numerous colors, stitches and patterns can be used in granny squares; however, all granny squares are constructed in basically the same way. Granny squares are worked by first crocheting a ring of chain stitches at the center of the square and then working outward. The finished square is generally made up of a series of rings around the inner chain stitches.