To learn how to compile libguestfs from sources:

  guestfs-building(1)  or  http://libguestfs.org/guestfs-building.1.html

To learn how to extend libguestfs:

  guestfs-hacking(1)       http://libguestfs.org/guestfs-hacking.1.html

To learn about the architecture and internals of libguestfs:

  guestfs-internals(1)     http://libguestfs.org/guestfs-internals.1.html

To learn how to write programs using the libguestfs API:

  guestfs(3)               http://libguestfs.org/guestfs.3.html
  guestfs-examples(3)      http://libguestfs.org/guestfs-examples.3.html