How can I insert a node with value 'val' as the n'th node to a Linked List?

I am doing a programming task on Python right now. I have to complete this method:

    def add_position(self, n, val):
        """Insert a node with value 'val' as the 'n'th node."""

        if n < 0 or n > self.get_size():
            raise IndexError("List index {} out of range".format(n))

I have worked on this method many hours but I really can't get what to do here. Can someone help me?