This document provides an overview of the key components and features of ExpressionEngine, including custom fields, channels, templates, tags, variables, add-ons, and some EE puns. It discusses how custom fields and channels are used to define content types and fields, how templates are used to display that content, and how tags and variables are used to output content in templates. It also briefly introduces common add-on types like plugins, extensions and modules that extend EE's functionality.