How do I declare/create a structure?

In general, you don't ``declare'' a structure. Just use a (probably anonymous) hash reference. See the perlref manpage and the perldsc manpage for details. Here's an example: 

    $person = {};                   # new anonymous hash
    $person->{AGE}  = 24;           # set field AGE to 25
    $person->{NAME} = "Nat";        # set field NAME to "Nat"

If you're looking for something a bit more rigorous, try the perltoot manpage.