Click here for the help pages on photos.
To edit the details on a photo, click the "view/edit" link in its caption. This takes you to the Edit-Photo Page.
From here you can add or change the title, people and things identified in the photo, or change the location and date. You can also add comments.
If you click on the image at the top of the Edit-Photo Page you'll see the image at its full size.
See the Photos FAQ for more.