How does CQ5 work?

CQ5 has two instances Author instance and Publish instance.

Author instance: This instance is what Business users use to edit the content , look and feel of the website. The components created often have dialogs(extJS interface to edit the component) for the editors to configure stuff, all of this limited only to author instance. Once the editors have configured the content, CQ allows the editor to publish the content. When the pages are published the page gets replicated to the configured publish instance. CQ allows creation of complex workflows for business needs that have a hierarchy for content authoring.

Publish Instance: This is the instance that visitors to the website will access, none of the dialogues that editors can access are available in this instance. All they will see is published pages and will have no clue about the editable nature of the page.While publishing pages the editors can mention the time period for which the published page should last.
Usually there is a caching mechanism called Dispatcher between publish instance and visitors of the site.

CQ5 tutorials