Each square is the equivalent of one single crochet stitch. To begin chain the number of stitches (numbers on the bottom of the chart) + 1 then insert the hook in the second ch from the hook. Sc in each stitch across changing yarn colors where indicated on the graph (there is a link to a tutorial for changing yarn). After you do the last sc, ch 1 and turn and start the next row. The yarn is carried under the stitches. There are links to tutorials on how to do tapestry crochet.