Primary Sources:  actual records that have survived from the past, such as letters, photographs, articles of clothing, catalogs etc.
Websites that provide Primary Sources have a (P) after the website title.  

Secondary Sources:  accounts of the past created by people writing about events after they happen.
Websites that provide Secondary Sources have a (S) after the website title.

Websites that provide both Primary and Secondary Sources have a (P/S) after the website title.