Question

below, it says $ sign refers to jQuery. i need help understand how?

jQuery(function($){
    // Here `$` refers to jQuery
});

Answer 1

When you pass a function to jQuery like this:

jQuery(function() {
    ...
});

It’s the same as using jQuery’s “document ready” handler:

jQuery(document).ready(function() {
    ...
});

however the argument passed to that function is actually the global jQuery object itself – it’s just that most such handlers never use that parameter. Hence the real signature is this:

jQuery(document).ready(function($) {
    ...
});

so, within that function $ is a local alias to the global jQuery object. The variable name could be anything you wanted, but $ is a popular alias for jQuery, and the default global alias unless you call jQuery.noConflict().

This is described in more detail in the paragraph “Aliasing the jQuery Namespace” at http://api.jquery.com/ready/