EasyLayouts installs as a normal Joomla package and adds the following to your site:
A component used to create and manage your layouts
A system plugin that allows EasyLayouts to act as a template overriding system in the frontend
A special file to allow EasyLayouts to 'wrap' modules you want to override - this file is placed in the modules folder but isn't a module that can be created independently of EasyLayouts
A few extra custom field types - at the time of writing these include:
EasyLayouts Related Article - allowing you to associated articles with each other
EasyLayouts Embedded Video - allowing you to include YouTube and Vimeo videos in your articles
More to follow
The plugins are all automatically enabled during the installation process.