Rakudo: Revision 4
To build the Rakudo Perl 6 compiler, first get a working copy of Parrot, then change to the languages/perl6/ subdirectory and type "make perl6". This will build an executable.
To run a program with Rakudo Perl 6, issue a command like
$ perl6 hello.pl
Or, to run an interactive perl6, type
For additional build instructions, you might also have a look at this PerlMonks post.
parrot changes rapidly, and rakudo as well; if you have issues with the latest point release, be sure to try svn-latest of parrot/rakudo.