Pictures are aranged in sheets of thumbnails which you can navigate with the RIGHT and LEFT buttons to go from page to page of thumbnails or use the UP button (or LEFT from the first or RIGHT from the last) to return to the previous index page.

Then just click on a thumbnail to get the full sized picture, navigate with the RIGHT and LEFT buttons to go from full sized picture to full sized picture or use the UP button (or LEFT from the first or RIGHT from the last) to return to the referring thumbnail sheet.