there two types of galleries built-in to the MonoX, Photo Gallery a more specialized one oriented exclusively to Photos, and there is a File Gallery a more generic one where you can upload any kind of file form videos and photos to documents.
Photo gallery sample can be found here
, while File gallery sample can be found here
. For the File gallery you should register and go to the Site Wall or your profile Wall, then try to upload any kind of files and you will get the File Gallery preview.