They don't do the same things.
In a default standard Windows setup the left-key opens the Start-menu and is used in various combinations (E.g left-WIndows-key+R open the Run-prompt) as short-cut key.
The right Windows-key functions the same as the right mouse-button key on your mouse.
EDIT:
In all my 35 years of using computers I have never seen, or even heard of, a keyboard having 2 Windows keys.
I have seen plenty of keyboards with the right-key (menu-key) labeled as a 2nd Windows-key.
Seems such keyboards do exist, but I honestly didn't know that.
I didn't pay enough attention to the picture. My bad.