This week's book giveaways are in the iOS and Features new in Java 8 forums. We're giving away four copies each of Barcodes with iOS: Bringing together the digital and physical worlds and Core Java for the Impatient and have the authors on-line! See this thread and this one for details.
The first one is an empty reference - a null reference if you will. So no, you can't call orderList.add(order); on it because you would get a NullPointerException, (unless you assign an object to it between the variable definition and method call).
The second one actually creates an Object of a suitable, concrete implementation of List, and so can have a method called on it without an error occurring.