Hold right sides together of two of the granny squares. Thread a strand of yarn in color A on a large-eye needle. Sewing through both thicknesses, join the two squares by sewing through the back loops only, joining one side edge of the squares. End off. Weave in ends. Unfold these two and place the third square on one of the squares again, with right sides together. Sew these two squares together, joining one side edge, in same manner as before. End off. Weave in ends. Unfold.
The next round uses long sc. Here's a link with closeup photos and a how-to: http://crochet.about.com/library/weekly/aa042598.htm
Outside Round: Attach color C in back loop of corner st on right-hand top of the joined granny squares. Work in back loops only for entire round: ch 2, * sc in ea of next 3 sc of granny square, next, make a long sc by inserting hook in the very center hole of the granny square (refer to photo), yarn over hook, draw this loop through the center hole and draw the loop up to the level of the height of the previous sc of this round, complete as a single crochet, then sc in ea of next 6 sc, long sc in center hole of next granny square, in same method as before, then sc in ea of next 6 sc, long sc in center hole of next granny square, sc in ea of next 3 sc, ch 1 for the corner, sc in ea of next 3 sc, long sc in center hole of same granny square, sc in ea of next 3 sc, ** ch 1 for corner, repeat directions between * and ** once, then sl st in beginning ch-2. End off.
