Inheritance lets you create a new class based on an existing one. The new class automatically gets all the members of the original, plus any new members you add. This saves you from rewriting code.
Think of a Car class inheriting from a Vehicle class. Car gets everything Vehicle has like speed and fuel, then adds car-specific features like trunk size. The relationship is "Car is a Vehicle".
Without inheritance, you'd copy-paste code between similar classes. Changes would require updating multiple places. Inheritance centralizes shared behavior in one location.