I recommend that you get your hands on some good documentation. Perldoc ("perldoc perl" on your commandline/shell) will be always helpful. I also recommend Beginning Perl (available online), which is a really good book for Perl beginners.
Had I posted this, I would have lost all my points! Anyway, here is the explaination:
my = declare a variable.
$data = variable name.
() = similar to shift or pop.
@_ = an array that you populate and send it off to a sub routine or a function.
Example
$var = 'some sort of data';
&My_Sub($var);
sub My_Sub
{
my($data) = @_;
Print $data . "\n";
}
output:
some sort of data