when you press "post" theres a bar that says "Browse" you can upload the image there by selecting the file on your computer, or you can have it hosted by going here: http://www.imageshack.us/ and choosing to upload the file the same way from there (only it lets you pic your resolution-...size of pic)
hope that helps!!
If you want use this thread as a test thread for you to learn on !! we can always delete it when your done if you so wish...and you can use the "edit" button to fool around with it after you post too
also I want to draw your attention to the IMG button on the top right of the posting window...from there you can press the tag, insert an address of the image, and press the button again to close the tag