right click on the image.
from the options click 'copy image location' ... that's the URL.
paste that into your reply box here. then put those tags around it i mentioned
[I assume it's from a webpage since your first attempt was a facebook url?]
any image from a webpage has it's own URL ---> it ends in .jpg
if it's from your PC, then it doesn't have a url and you'll have to upload it to an image hosting site like imagur or imageshack to be able to post it here, since the forum image posting option is disabled/broke and it doesn't host images for you unfortunately