1. Move mouse pointer to bottom right of screen to bring up the Charms Bar.
2. Left click on Search.
3. Make sure Apps is highlighted.
4. Type File Explorer into the search box until you see the
File Explorer icon on the left.
5. Right-click on the File Explorer icon then click on
Pin to taskbar (at bottom of screen).
(the above are instructions for when using a mouse - same principle applies for touch)