Linked List Assignment Operator C++

Question

Trying to implement an assignment operator for a doubly linked list class.

I think part of my problem with this is I do not completely understand how assignment operators work. Here is what I have currently:

//assignment operator
Set& Set::operator=(const Set &rhs){

    _head = rhs._head;
        _tail = rhs._tail;

        //null, basically this object is 0
        if(rhs._head == NULL){
            _head = NULL;
            _tail = NULL;
            _size = 0;
        }else{
            _head = new Elem(*rhs._head);
            _tail = new Elem(*rhs._tail);
            _size = rhs._size;

            Elem *prev = NULL;
            Elem *curr = _head;
            Elem *otherCurr = rhs._head;
            int counter = 0;
            while(otherCurr->next != NULL){
                curr->next = new Elem(*otherCurr->next);
                curr->next->prev = curr;


                curr = curr->next;
                otherCurr = otherCurr->next;
            }

            //now that we are done lets setup the tail
            _tail->prev = curr;
            curr->next = _tail;



        }

        return *this;

}

Not sure if it will be needed but here is my .h file. The _head and the _tail variables are dummy Elements, and POINT to the first and last elements.

Here is my .h, well just the important part of it:

struct Elem {
        ELEMENT_TYPE info;
        Elem *prev, *next;
    };
    Elem *_head, *_tail;
    int _size;

Any sort of help would be incredible. At a loss here...