Unlike many content management systems which maintain content in a haphazard manner, Sitecore maintains data in a structured content tree.
Data is represented as items. These items of different types are combined in a tree structure such that an item can have a parent and child items.
Templates are like Object Oriented Classes. A template contains fields that contain the actual content for an item. An item is an instance of a template just as an Object is an instance of a class. A template can have a “Master” which is used to create an item of a template. A master plays the same role as an Object Oriented Constructor. Masters can be configured to specify default values for fields and can specify sub-items that should be created when an item is first created. Templates can be based on other templates and inherit their fields, much like Object Oriented inheritance.