[Returning value from Stored Precedure]

I have this stored procedure that has 2 parameters, the first one is the cartId(which is the IN) and I have the newOrderId(which is the OUT). Now,
I know that the inCartId is the cart id which will come from the form or whatever means the cart is been access but I don't understand the OUT 
newOrderId since that is what MySQL will return. 
Now, in the PHP calling this Stored procedure, it will look like this.

$sql = 'CALL create_order(:cart_id, "What will be here")// The cart_id is what PHP will pass to MySQL, but what will be passed
to the 2nd argument since does not before hand what MySQL will return.

CREATE PROCEDURE create_order(
    IN inCartId int,
    OUT newOrderId int
)
BEGIN

    -- Insert a new record into orders and obtain the new order ID
    INSERT INTO orders (created_on) VALUES (NOW());

    -- Obtain the new Order ID
    SELECT LAST_INSERT_ID() INTO newOrderId;

    -- Insert order details in order_detail table
    INSERT INTO order_detail (
        order_id, product_id, attributes, product_name, quantity, unit_cost
    )
    SELECT
        orderId,
        p.id,
        sc.attributes,
        p.name,
        sc.quantity,
        COALESCE( NULLIF( p.discounted_price, 0 ), p.price ) AS unit_cost
    FROM
        shopping_cart sc
        INNER JOIN products p ON sc.product_id = p.id
    WHERE
        sc.cart_id = inCartId
        AND
        sc.buy_now;

    -- Save the order's total amount
    UPDATE
        orders
    SET
        total_amount = (
            SELECT
                SUM( unit_cost * quantity )
            FROM
                order_detail
            WHERE
                order_id = orderId
        )
    WHERE
        id = orderId;

    -- Clear the shopping cart
    CALL shopping_cart_empty(inCartId);

END

 

[Referencing The Event]

oh sorry Larry for disturbing you as I have grasped the ideas of referencing events after posting.

 

Albeit, I want to know if you have any book written on Phyton?

[Referencing The Event]

in chapter 8, larry talks about events and referencing them. I need more examples on how to reference the event