My doubt it how to access this display method using the object.

First you create an object calling class method new

my $foo = Employee->new;
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Then you call the object method display, on the object $foo

$foo->display;
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I suggest you review carefully the book/tutorial which taught you about package ... because calling methods is basic syntax.

Its covered in various places, including the free book Modern Perl a description of how experienced and effective Perl 5 programmers work....You can learn this too.

Also, FYI, you have a question, not a doubt, see "Question" vs "Doubt"