Sometimes the browser has an issue with the upload. I see that from time to time. I can usually get the upload to work by either trying with a different browser, or just clicking refresh on the page and trying to upload again. Sometimes it takes a couple few tries but goes through. You should see a progress bar and then confirmation that the file is uploaded.
Once uploaded, you can post any of your uploaded photos by pressing the XIMG button when you reply and selecting the image you want to put into your post.
Once uploaded, you can post any of your uploaded photos by pressing the XIMG button when you reply and selecting the image you want to put into your post.