Method provided by component may need to be implemented, What does this mean?
I am also not entirely sure what it's saying, but to me, it sounds like this is saying that in inheritance, if e.g. the Dog class already has function bark() { print('woof!')}, then the person writing a GoldenRetriever class which inherits from Dog doesn't need to write a bark method since it's inherited from Dog.

On the other hand, if someone is writing a GoldenRetriever class that contains an instance of Dog inside each instance of GoldenRetriever, you will have to define function bark() { this.dog.bark() }.