They are really simple to use, I have used both Photobucket and Flickr with the later one being the one I used to most just because Flickr seems more stable and quicker than Photobucket, from my experiences at least. Pretty much all you do is upload your photo from your computer to whatever site you decide to use and from there pull up the code of that picture and insert into the "insert image" box here. Most of these site do have a free version but usually limit you on how many pictures you can upload along with the size of them.