What he's saying is that you have to have it uploaded to the 'web' somewhere and then 'refer' to it - you can't just add it to your post.
Set up an account with any picture hosting service and upload your picture to their site. You can then post a link to the picture by typing the web address into your post - like this:
http://www.fototime.com/051B16C37597BEE/standard.jpg Click the link and you open a new window including the picture.
Or you can click the little IMG button and type the same link into the window which pops up - this tells the board software to show the link as a picture - like this:
Showing the picture, rather than posting a link, does take up board space however.