"Lite Gallery" is a standard package for Concrete5 CMS and it is install as usual package. Just go to your Dashboard->Extend Concrete5->Add Functionality and click Install near the "Lite gallery" title.
Lite Gallery Install

This package containce of a general block and some of dashboard pages for customizing your gallery properties. After installation step, you can see a new page in bottom of dashboard under "Lite gallery" name. This page containce of basic properties of a galleries: name, description and images. Here you can add or remove galleries to the system and add or remove images from them. 

Lite Gallery Properties