I am having a trouble in understanding the Example 4.7 (pages 65-66), the genus two fibrations with $p_g=0$, $q=1$, and $K^2 = -3$, in "Surfaces fibrées en courbes de genre deux", Lecture Notes in Mathematics, 1137, by Xiao Gang(http://link.springer.com/book/10.1007%2FBFb0075351). a My French is not good and the Google translator confused me even more. If you are familiar with this construction, could you please outline it?

Especially, I don't understand how the branch divisor $D$ is defined on page 66. Also, does it follow from the construction that the fibration admits $-1$ sphere section? Thanks in advance.

Note: The above fibration is obtained from $\mathbb{CP}^2\# 7(-\mathbb{CP}^2)$ by taking two fold branched cover along a certain degree six divisor $D$, where the divisor $D$ is constructed by considering a complete quadrangle in $\mathbb{CP}^2$.