Next, click on the "Configure App" link at the right of your screen. That brings you into the ArcGIS Online story map builder mode where you can start adding content. For images, it's easiest to use photos already posted publicly on Flicker, Facebook or Picasa. If your photos are somewhere else, though, you can create a CSV file with column headers "Name, Caption, Icon_color, Long, Lat, URL, Thumb_URL". For more info, download the sample CSV template.