Div class and Div ID - Differences

• Div ID making up main content of the page
• Div Class can be applied to many things on the page

-use id whenever you want to refer to a specific element and class when you have a number of things that are all alike. 

id elements are things like header, footer, sidebar. Common class elements are things like highlight or external-link.

SOURCE:

https://stackoverflow.com/questions/544010/whats-the-difference-between-an-id-and-a-class