A primary source is a document written by someone who witnessed the event personally. A secondary source is written by someone who wasn't there. Somethings that they have in common are that they both involve people. Also, they both can be written in a document. A primary source is different because is uses diaries, speeches, letters, interviews, news film footage, autobiographies,etc. An example of a primary source is the "Diary of Anne Frank - Experiences of a Jewish family during WWII." A secondary source is different because it uses textbooks, magazine articles, commentaries, encyclopedias,etc. One example of a secondary source can be any kind of history textbook. Primary and secondary sources are helpful because you can have a witness say what went on.