I quote the following paragraph form Kollar-Mori on page 22:
Let $X$ be obtained from $P^2$ by blowing up at the nine base points of a pencil of cubic curves, all of whose members are irreducible. Choosing one of the nine points as the zero section, we get an infinite group of automorphisms of $X$ generated by the other eight sections. So $X$ has infinitely many (—1)-curves, all of which span an extremal ray of NE(X). $|-K_X|$ is the elliptic pencil, thus $-K_X$ is nef, but not ample.
I have following questions in understanding this paragraph:
(1) What does it mean by taking one point as a section? And why from this we can deduce the autommorphism group is infinite and there are infinitely many $-1$ curves.
(2) Why we can deduce that it is nef but not ample?