The thumbnail gallery on the product page can be used to display multiple images of the product. Although the position of the gallery varies by theme, it is usually just below the main image on the product page. When a thumbnail is clicked, the image appears, by default in a popup window that allows you to browse through the images.
Light Boxes and Sliders
Many stores use a third-party light box or slider to display product images in a more elegant fashion. Typically with a light box, whenever a thumbnail image is clicked, it replaces the main image on the page. You can use the left and right arrows in the light box to browse through the images, or click a thumbnail to view a specific image. When zoom is activated, you can click the main image and move the cursor around to magnify different parts of the image. The magnified selection appears to the right of the image. You can find a variety of light box and slider extensions available in Magento Connect.