algorithm - Java Queue Implementation with Pointers

I need help understanding this. I know how to implement the queue but there is one small part bothering me. I drew on my notebook the flow of how things work but I don't get how the head has a nextNode without me setting it. How does the head end up pointing to the next node?

public void enqueue(T data){
        count++;
        Node current = tail;
        tail = new Node<>(data);
        if(isEmpty()) {

            ///////////////////////////////////////////////////////////////////////////////
            // when this runs, doesn't head.getNextNode point to null?
            // if the list is empty, then tail is null.
            // On the deque method, I can sout head.getNextNode() and I get data back, how?
            ///////////////////////////////////////////////////////////////////////////////
            head = tail;

        } else {
            current.setNextNode(tail);
        }

    }

Below, the dequeing works fine, I think I'm having an issue understanding the whole reference/pointer thing

public T dequeue() {
        if(isEmpty()) {
            return null;
        }
        count--;

        T dataToRemove = head.getData();
        /////////////////////-+{[UPDATE]}+-////////////////////////////////
        // WHERE DOES HEAD GET THE NEXT NODE FROM? THIS WORKS, BUT WHERE IS
        // THE NEXT NODE COMING FROM IS WHAT I'M ASKING?
        ///////////////////////////////////////////////////////////////////
        head = head.getNextNode();

        return dataToRemove;
    }