Crocheting a granny square requires knowledge of two different stitches: chain and double crochet. Each round is comprised of making shells of three double crochet stitches separated by two chain stitches. Each subsequent round is crocheted into the chain two hole of the previous round. Use a hook size appropriate to the yarn of choice.
Begin by chaining five, and join with a slip stitch to create a ring, or use a magic ring. All stitches in round one are crocheted into the center of the ring.
Chain three stitches, which count as your first double crochet in the shell. Double crochet two more stitches. Chain two, and work one shell. Repeat this sequence twice more. Chain two, and join to the first shell with a slip stitch to complete round one.
Chain three stitches, and turn the work around, then work two double crochet into the two-chain hole created from the previous round. Chain two, and work one shell into the same two-chain hole, which creates a corner. In the next two-chain hole created from round one, work one shell, chain two, and work one more shell for another corner. Repeat twice more, and join the final chain two to the first shell with a slip stitch.
Chain three, turn the work around, and work two double crochets for the first shell. Work one shell in each chain two hole created from the previous round except on the corners, where two shells are worked per corner separated by a chain two space.
Repeat rounds until the square measures 7 inches across. Remember to turn the work at the beginning of each round so the first shell is worked into a hole from the previous round.