Answer 1

Charles Zolina See virtual functions in the base class can either have a definition or they might not.
But a pure virtual function doesn't have a definition in the base class, and if you have even a single pure virtual function in a class then the class has to be declared abstract.

Purpose of using virtual function is to give privilege to the sub class to override them. And they come under run-time polymorphism.

Answer 2

Charles Zolina This will help you understand what are classes and objects.

Edit: OOPS is vast so tell us what part you don't understand because explaining the whole oop is difficult.

https://www.sololearn.com/Discuss/2075135/?ref=app

Answer 3

Charles Zolina you're welcome