The images that you see on the sites are folders. By clicking the photo you will open the folder.
By clicking the photos in the folder you will now see the large version of the photo. You can now continue in a slideshow if needed.
If you want to browse the photos on fullscreen, click the square on the right-hand side lower corner.
You can exit the fullscreen mode by clicking the same square or the esc-button on your keyboard.
Browsing trough the photos with the arrow-keys is also possible.