Primary sources include original documents, photographs, interviews, and so forth. For example, if you are writing a paper about the book "Lord of the Rings" then the book itself, an interview with the author, and could serve as primary sources of evidence.

Secondary sources present information that has already been processed or interpreted by someone else.  So, for the same paper, a book review from a magazine or a collection of essays about the book would be secondary sources.

Depending on the context, the same item could be either a primary or a secondary source: if I am writing about people’s relationships with animals, a collection of stories about animals might be a secondary source; if I am writing about how editors gather diverse stories into collections, the same book might now function as a primary source.