Okay, I'll give it a shot.
To post a pic that's on your computer, you can use the "upload attachment" feature that is at the bottom when you open a "post reply" window. Click "upload attachment" and you'll see "filename" and "browse" to the right of it. Click "browse" and a window listing what's on your computer will appear. Double click on the photo you want to post. Then click "add the file" located beside the browse button. You'll then see a window with "Place inline" - use this if you want the pic to appear in the body of your message. Here's an example of how that will look:
This is how the attachment (photo) will appear if you don't place it inline:


