This procedure can be used anywhere in the forums.  This example uses the "For Sale or Trade" catagory...

1. Login using your username and password.
2. Click on the Forums menu
3. Scroll down to "Items for Sale or Trade" and click on it.
4. Click on the "New Thread" button.
5. Put a title for your listing the the SUBJECT line.
6. Put your listing in the big text box below.
7. If you have a picture or other attachment:
     A. Click "Upload New File" in the "Attachements" area
     B. Click "BROWSE", then go find your file
     C. Click "Upload Selected File"
8. Finally, at the bottom of the page, click "SUBMIT" (or "preview" if you want to look at it first)