What is Open File ? How to win ?

If there is not any pawn on a file, this file is called " Open File" .  You have to take control of this file by using at least one of your Rooks and your Queen.  As you see in the diagram No.1 d-file ( green one ) is an Open file.

This position is from the game Karpov - Seirawan:

Black controls the open file with 2 Rooks and the Queen.  See it in diagram 2 

      In order to see how to win   in this position , you can watch  the annotated game in  my Youtube video :  https://youtu.be/9KltjHhLHjI