Do you understand the difference between inheriting a class and implementing an interface?
When you inherit a class the derived class basically IS the same thing as the base class with some extra functionality, e.g. if Class1 has functionality A, B and C then if Class2 inherits Class1 it also has functionality A, B and C. That functionality can be modified or added to but by defualt it is the same.
An interface describes a set of functionality that all implementors will provide. It provides no implementation itself, unlike a base class. It is completely up to the implementor how the functionality is provided. Implementing the interface simpy guarantees that it will be provided. This allows different classes that may be very diffreent in many ways to be treated in exactly the same way for the specific subset of their functionality defined by the interface.
Inheriting a class and implementing an interface are independent operations, except that if you inherit a class that implements an interface you cannot explicitly implement that same interface yourself.