The Data Dumper module let's you visual how data is being interpretted by Perl. You may need to install the Data Dumper module on your system. Then, you will tell your Perl script to use the Data Dumper module.
As a very simple example, let's say your script has a variable ($foo) and you want to understand what value $foo contains. You can use Data Dumper to examine $foo.
print Dumper $foo;
In this example, Data Dumper let's you know that $foo contains a value of Hello World.
$VAR1 = 'Hello World';