What does this c# syntax is for?

I am unaware of C# concept which is defined below.

I have following code below but i am unaware of what exactly is the use of last new DecoratorB( new DecoratorA(component)) in the Main function.

1) Can you please explain me what exactly the above code is doing and how references are set for a given object.

2) Also Display(string s, IComponent c) accepts IComponent as parameter so what exactly does the DecoratorA and DecoratorB class returns.

 static void Display(string s, IComponent c) {
     Console.WriteLine(s+ c.Operation( ));
 }

 static void Main(){
     IComponent component = new Component( );
     Display("1. Basic component: ", component);
     Display("2. A-decorated : ", new DecoratorA(component));
     Display("3. B-decorated : ", new DecoratorB(component));
     Display("4. B-A-decorated : ", new DecoratorB(
     new DecoratorA(component)));
 }


interface IComponent {
 string Operation( );
 }

 class Component : IComponent {
 public string Operation ( ) {
 return "I am walking ";
 }
 }

 class DecoratorA : IComponent {
 IComponent component;

 public DecoratorA (IComponent c) {
 component = c;
 }

 public string Operation( ) {
 string s = component.Operation( );
 s += "and listening to Classic FM ";
 return s;
 }
 }

 class DecoratorB : IComponent {
 IComponent component;
 public string addedState = "past the Coffee Shop ";

 public DecoratorB (IComponent c) {
 component = c;
 }

 public string Operation ( ) {
 string s = component.Operation ( );
 s += "to school ";
 return s;
 }

 public string AddedBehavior( ) {
 return "and I bought a cappuccino ";
 }
 }

Also if i am missing a basic then please guide me to the required link

Thank you