What does "=>" mean in PHP?

It is used to access static methods of class, static variables and constants

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It's the 'Scope Resolution Operator'.

The Scope Resolution Operator (also called Paamayim Nekudotayim) or in simpler terms, the double colon, is a token that allows access to static, constant, and overridden properties or methods of a class.

http://php.net/manual/en/language.oop5.paamayim-nekudotayim.php

In layman terms it is used to call static Methods of a Class.

In your example, LoadMenu() is a static function of the TestPages class.

This means that you do not have to create an instance of a TestPages to call LoadMenu()