You need a hosting site such as Photo bucket. After that, this article will explain it better than I can.
doogsmodels.com/.../how-to-post-your-photos
Things have change a little since this was written. The link you use to add the URL is the one to the left of the one indicated in the article.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3