A gallery is made up of several parts. The Gallery Thumbnail, the Gallery Picture, the Caption, and the Keyword and Projects. You do not need to have all parts, and each part can be placed separately from the others, however in order for the Gallery to function, you need to at least have the thumbnail and the large image sections, as well as at least one of the Keyword or Projects selector.

Gallery Overview

The gallery allows you to display a series of pictures that are related by either Project or Keyword. The thumbnail strip allows you to see several images at a glance. The large image allows you to look at one image in better detail.
(see image below for example)