davido has already explained perfectly how to analyse the existing structure. Just for completeness, here is how you'd build this up yourself. Two ways are shown, one using "ordinary" structures and taking references to these, the second by building the final structure up directly with anonymous hash/array references:

# 1:
%item = ( title => 'SomeTitle',
          link  => 'http://somelink' );
push (@items,\%item);
%rss = ( items => \@items );
$rss = \%rss;

#2:
$rss = { 
         items => [
                    { 
                      title => 'SomeTitle',
                      link  => 'http://somelink'
                    }
                  ]
       };
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