BarriedaleNick can explain it really well, but the site won't let me look for his reply to someone asking the same question.
I am not too bright about it, but managed to make it work recently. So: get a Photobucket account (free) and it lets you load your pics, then there are instructions on the site about how to get the pics from there to any forum, such as here!
Have a play, and hopefully someone will be along in a minute to explain properly