click on Galleries on the menu bar above. When that new page opens on the far right hand side of the menu bar is a link to upload photos. Click it and all should be obvious.
To avoid the wrath of a mod do ensure you resize any photo's you upload to be no more than 800 pixels on the longest edge, unless a pano, in which case 1000 pixels is allowed. I think there's also file size limit, maybe 200kb, but I can't remember. The upload page will tell you I'm sure.
Hope that helps...