Much of what we know about history comes to us from secondary sources. An author or reporter gathers the information by looking at documents from a certain time period. They then process it and write a historical account for us. What we then read about history comes to us through that author or reporter's point of view.
Sometimes, when you look at the original documents yourself, you form a different impression. These documents are considered primary sources, because they have not been filtered through another reader/writer. They are actual records of the time. They include letters, news accounts, books, photos, pictures, and other pieces of information that were created during a particular time. By taking a close look at them, you can see history through your own eyes.