Simple: $self->{friends} = ['John', 'Marie'];, or to add something to that list: push(@{$self->{friends}}, 'Jane');.

Same story for hashes: $self->{pets}->{dogs} = 'mike'

You may want to have a look at the tutorials on references and data structures in the perldocs (since the site is down, I can't link you now).

Hope this helps, -gjb-