The preview screen displays a larger version of the selected image as well as more details about the image such as it's description, owner etc.
If more than one image was returing from the search query then to the right of the preview image there may be one or two thumbnails showing the previous and next images returned in the search. Clicking on either of these two thumbnails will display the preview page for that image.
If the image is for sale then the cost of the prints for that image can be obtained by either clicking on the 'Show Prices/Add to Order' button or simply clicking on the image. which will cause the 'Purchase' screen to be displayed.