Can someone clarify when to use underscores? edit

If I choose a random page—Bill Clinton—and follow the script's logic, I would be removing the underscores from an image link.

[[File:Bill_Clinton_1995_im_Parlament_in_London.jpg|thumb|left|Clinton addressing the British parliament on November 29, 1995.]]

 
underscores in image/file path

The image would still work as a link/image but I'm a bit confused as to which is the proper method; to have underscores for this situation or to not have them. Can someone take a look and or point me in the right direction to better learn the markup and syntax rules?--GabeLee (talk) 07:32, 28 October 2016 (UTC)Reply