The secondary source is a later report or discussion or a textbook. Both primary and secondary sources can be altered to favor a certain point of view, so should be used with caution. School textbooks, encyclopedia articles and the like are generally compilations of several secondary sources and are therefore tertiary sources. Let's imagine I want to know what you had for breakfast this morning. There are a number of ways I could find out. For instance I could ask one of your friends or I could ask a relative. The information I gained as a result may well be true. However, if your friend wasn't there at the time their information might be wrong. If I choose to believe that person I'm accepting a secondary source. What can I do to make sure that the data I get is as accurate as it possibly can be? Obviously I need to ask YOU what you ate for breakfast. You are my primary source for that information. Likewise if I want to know when the Second World War ended I'd do better to speak to someone who actually heard Attlee's or Stalin's or Truman's declaration than to ask my friend who sits next to me and who was born decades later. But suppose I want to know about the life of Anne Boleyn. Bearing in mind there's no one alive who knew her back in the 16th century I can't go to her or any of her friends and ask them directly. Any book written about her at the actual time would be considered a primary source, likewise something that belonged to her -- the closer it is to her the better.