Hi Paul
click 'tools' on the forum toolbar. Then click 'help' and then 'enhancing or editing post'. You'll get the official directions
Orrr you can listen to me
When you're making a post across the top is a tool bar. The last box in the bar has a paperclip on it, click on that. A window should open enabling you to post an attachment. (Assuming that is, Chris has enabled attachments.)

BTW, nice avatar!

Keep'em flying