To whipstitch (point de surjet in French), hold 2 hexagons together, right sides facing. Knot your thread and insert the needle under the fold so that it comes out on the corner. Sew straight across the edges. If you have difficulty pushing the needle through, or if you are catching the edge of the paper, your fabric is basted too tightly over the papers.
You can add a hexagon, and then run your needle back under the fabric to sew another side - see the steps of photos below. Stitches are 1/16th" apart (2mm).
On the front the stitches appear straight across, and on the back they appear slanted - on these 5/8" hexagons there are 10 stitches, including the one on the end. More stitches is not necessarily better - too many stitches can create a ridge and weaken the fabric.