The main distinction between primary and secondary sources is how far removed they are from the event they are describing.
Primary sources are first-hand accounts written at the time of an event or maybe shortly afterwards. They are the first telling of something that has happened, and are tellings by those who witnessed or experienced the actual event. Primary sources can be works that are unpublished such as letters, memoirs, diaries, art, photographs, maps, video, audio recordings, speeches, interviews, etc. They can also be works that are published such as newspapers, magazines, research reports, or published interviews and stories. There usually are not a lot of copies of primary sources.
Secondary sources are published after primary sources and their purpose is to interpret or talk about the events that were described in primary sources. They are second-hand accounts of an event and are a further step removed from an event than primary sources. Primary sources can include journal articles, newspapers, magazines, books, textbooks, and documentaries. There are usually a lot of copies of secondary sources available.