The Structure theme front page is supposed to look like this: http://en.blog.wordpress.com/2010/04/27/new-theme-structure/
The photo in the big box at the top is the Featured Image from the latest post in the category you specify under "Appearance > Theme Options" panel.
To set this up, first choose a category you want to use with this, under "Appearance > Theme Options". You can call this category "Featured" or "Front Page" - a link to the latest post from this category will always be prominently displayed in the front page.
Once you have a category selected, choose a featured image for the latest post in that category. This image will be displayed in your front page. To set a featured image, see here:
Remember that you have to choose a featured image for every post you put in this category.
For more information about Structure, see this post:
Let us know if you have any more questions - we'd be happy to help out.