(1) Don't start with a big photo! I usually resize mine to 900px wide. I use
(free) to resize my images most camera/smart phone images are way to big.
(2) Click browse, select the photo from your hard drive and click Open. Now you'll see the image file path in the Select Image file to attach box.
(4) Click submit on your post.
If you want more that one photo, I go back and edit the post. Then browse, open, submit. Rinse repeat.