CMS Made Simple Forums

With CMSMS 1.11.4 OOTB, how do we use the "URL" field located at the bottom of each article page in the News Module?

I tried typing in several things to use in that field, like the following...

my-page
or
http://mysite/my-page
or
mypage
or
/mypage

and every time I clicked Apply, a red box error popped-up on top of the admin article page saying...

Invalid URL (maybe it is already used, or there are invalid characters)

I'm assuming this field allows this specific article to have it's own custom URL. Is that correct?

Thanks