Can't understand part of code

[Kuzyo]

Hi, everyone.
Here I found tutorial with nice menu http://tympanus.net/codrops/2013/07/30/google-nexus-website-menu/comment-page-1/#comments, but can’t understand how works one part of the code. Here is full code http://codepen.io/anon/pen/GklED
Maybe somebody explain.

There is function with two arguments, but in code this function don’t recive any arguments, how this function works:

function gnMenu( el, options ) {
        this.el = el;
        this._init();
    }

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