Sitecore Data Structure
One key issue for Sitecore beginner is that so many different names and each concept is messed up with others. Check this diagram and video, hope it can make you calm down.
For Sitecore beginner, this would be a very good introduction to all the key concept of sitecore including.
•Template
•Content Item
•Layout
•Sublayout
•Standard Values
•Parameter Settings
•Data Source Settings
•Presentation Details