That code isn't creating an instance of an abstract class. And there's nothing unusual or mysterious about the fact that a subclass's constructor has to invoke a constructor of its superclass, even if the superclass does happen to be abstract. In fact nothing different happens when the superclass is abstract.
Yes because your subclass extends the abstract class. Every class (not interface, including abstract classes) has at least one constructor. In your case there is an implicit call to the superconstructor in base (which is added by the compiler).
"Any fool can write code that a computer can understand. Good programmers write code that humans can understand." --- Martin Fowler
Please correct my English.
My point is, there are rules for how constructors work, including how they call constructors of their superclass. And those rules are the same whether any of the classes are abstract or not. In particular abstract classes need constructors just like any other classes. So the answer to your question is "It makes no difference whether the superclass is abstract or not."
It's possible that you don't understand the rules and need to discuss them here. That would be perfectly normal for Beginning Java. But abstract classes don't come into that question.