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search for vtable explaination on learncpp.com. They have a good explaination with diagrams.

Every class has a hidden member pointer called vptr. Along with each class there is a static table called Vtable. The vptr points to vtable. Everytime an object is created, the vptr in that object points to the vtable for the class. The vtable contains pointers to the virtual functions.
The derived class inherits the Base class and along with it gets the vptr. However this vptr points to vtable associated with the derived class.
When we invoke a virtual function through the Base pointer, it always goes to the vptr. The vptr for the Base class object points to the associated vtable. The vptr for the Derived class points to the vtable of the derived class. And therefore they accesses the correct functions.

vtable for class A vtable for class B
=============== =============
&A::Foo &B::Foo
================ ==============

the vtable will look like this

A's Table will have function foo() address as defined in A class
B's Table will have function foo() address as defined in B class

Class A is abstract. Abstract class cant be instantiated because they will not have vtable.
Class B will have vtable having address to B::foo

class A vtable points to base virtual function A::foo()
class B vtable points to most derived function which is B::foo() (if there is one), otherwise it points to base virtual function too

V table will has v ptr which points to function definition. For pure virtual function, v ptr points to NULL.

No Vtable for class A
vtable will be created only for class B which stores address of function B::foo()