The content a page contains is defined by the 'page type' assigned to the page. A page type contains a number of custom fields, which are displayed when an editor edits a page. This page describes how custom fields and page types work together to help you sculpt your pages to contain whatever content you desire.
A custom field represents a definition for a single piece of content in a page. For example, using the Custom Field functionality found in Resources => Advanced => Custom Fields, you might create a field called 'page_title':
By assigning this field to a page type, you will see a field like the following when you edit a page using that page type:
A page type is a definition of the fields that make up a certain type of page/ resource. A page type is a collection of custom fields, which are assigned to the page type as follows:
Pages which use the above page type will present two fields: page_title and page_content. The other fields (page_category and page_intro) are not assigned to the page type, so they will not be available to pages of the 'Regular Document' type.