First download this library from CPAN:

L<http://search.cpan.org/~cmungall/go-db-perl/>

then:

  cd go-db-perl-X-XX
  perl Makefile.PL

you will be prompted with questions about your local go database
installation. If you do not wish to run the test suite, you can skip
these options (hit return)

Then type

  make install

You can then write programs that use the GO::AppHandle API, or you can
use the GOshell.pl script or any of the other scripts which have been
installed