scope resolution operator

Question

hi , I'm currently trying to gain a better understanding on the use of the scope resolution operator (::).
its my understanding that, when a class as been declared, a member or object of that class can be called using the (.) operator. However, I have seen the (::) being used for the same purpose.
Any clarification on the purpose of the (::) and the difference between the uses of both (.) and (::) would be greatly appreciated.
Thanks

Answer 1

scope resolution operator(::) is mainly used for accessing global variable.
For example :
int a=5;
int main()
{
int a=10;
cout<<a; //10
cout<<::a; //5
return 0;
}
hope it explains.

Answer 2

Would it be a case that, If I had a class A (see below) and wanted to use an object or member of that class within main, I would use the (::) operator to tell the complier that the member I want to access is within class A. Therefore, A::somefunction(); ?
ie.
class A {
public:
some_function();
};
int main()
{
A::some_function();
}
In such as case, even though the class members and objects are public, how come they do not operate as global functions and members?
Also, could I access the member by saying,
A.somefunction(); ?