Checking assignment operators with *this pointer

Hey,

I'am confused on the principles on checking a assingment operators
using This pointer. I understand using *this to access data member in
a class.

const B &operator=(const B& x){

          if (&x != this)
          a = x.a;

          else
          return *this;
}

  What i don't understand is the fact In this code i'am comparing &x
reference to the this pointer which i'am not sure what it is
containing or how it is comparing.

b1 = b2; in this line of code is b1 the reference and comparing itself
with b2?

below is code

thanks
-----------------------------------------------------------------

#include <iostream>
using namespace std;

class A
{
  int n ;

  public:
   A():n(0)
   {
   }
   A(int x):n(x)
   {
    n = x;

   }
  A(A &c):n(){

        n = c.n;
     }

   void print()
   { cout << n<<"\n\n";
   }

    A(const A& objectCopy){

            n = objectCopy.n; // copy constructor

    }
const A &operator=(const A x){
          n = x.n; // Operator

         }
         void good(){
          cout<< this->n<<"";
         }

   };

   class B
   {
    A * a;

int v;

     public:

    B(A & x)
      {

      a = new A(x);

        }

      void print ()
       {
         a->print();
         }
       B(const B& copy){ // Class B copy constructor
          a = copy.a;

         }
         const B &operator=(const B& x){

          if (&x != this)
          a = x.a;

          else
          return *this;

    // return *this;
          //delete a;
         }
         B::~B(){
             delete a;

                }

        };

//-------------------------------------------------------------------------=
=AD--

   int main()
      {

       {

        A a1(5);
       A a2(7);
        B b1(a2);
        b1.print();
        B b2(a1);
        b2.print();
        b1 = b2;
        b1.print();

   //a1.good();

        }

        cout << endl;
        int trick;
        cin >> trick;
        return 0;
        }