If you go to the "Gallery" page, then you should see an "Upload Photos" button or something like it. You can always ask the site administrator "Sim" or search for a help page.
I've clicked on that, and get as far as choosing photos to upload, but then when I hit the 'upload' button, it won't upload them. I'm gonna try and find a help page.
Make sure the file sizes of your photos are not too big. (I resize mine 4x6 inches at 72dpi and save them at a medium-high jpg compression - quality 8 on the sliding scale of 1 to 12).
If you don't understand what all that means, feel free to send me a private message by clicking on my login name. I work at a photo lab and should be able to help.