how to create and call a custom function in jQuery

Yes, because you declared the function within the scope of the first $(document).ready(function(){}) so it will not be available outside of that functions scope.

I am not sure why you would call $(document).ready() more than once. Try this:

$(document).ready(function(){
   function reload_cart() {
       alert('reload cart called');
   }

   reload_cart(); //i need to call from here.


   $('a.add_to_cart').live('click', function(e) {
       reload_cart(); //i need to call from here.
   });
});

Alternatively you can also declare your function outside of $(document).ready() and it will be globally available.

reload_cart is local to your first $(document).ready() callback. You can't call it from an outside scope.

You should merge your functions together:

$(document).ready(function() {
    function reload_cart() {
        alert('reload cart called');
    }

    reload_cart();

    $('a.add_to_cart').live('click', function(e) {
        reload_cart();
    });
});

An even better solution would be to create a cart object, add reload to its prototype, and initialize it outside of all of the callbacks.

Put your function definition:

function reload_cart() {
    alert('reload cart called');
}

Outside document.ready.

Currently, Its scoped inside the document.ready handler only.

$(document).ready(function(){
//reload_cart is only available here
    function reload_cart() {
        alert('reload cart called');
    }
});