The normal way looks like this:

perl Makefile.PL
make
make test
make install

For details see
perldoc perlmodinstall
perldoc ExtUtils::MakeMaker


If you don't have 'make' on your system,
then just copy 'MD5.pm' to a directory
named 'Digest/Perl/' in one of the paths
from @INC.

e.g. /home/lackas/usr/perl/Digest/Perl/MD5.pm

and insert a 'use lib' statement to your code:
use lib '/home/lackas/usr/perl/';
use Digest::Perl::MD5