Canon Community

I can't seem to find out what the extra plastic "guide" but not where to use it.  (I realize this is a newbie question and am embarrassed to ask the forum)

During my search, I keep finding people ask the differences between UFR II and UFR II v4, but it seems to go unanswered.  (I realize I may have missed finding the post with the answer, so let me apologize first).  Isn't there somewhere that we can fi...