You should simply pay attention to the date. Originality of the source. Certain types of research call for the use of primary sources of information. These are works that provide original information about a topic. Original experiments, historical letters and manuscripts, autobiographies, newspaper accounts contemporaneous to an event, and official records are examples of primary sources.
Secondary sources are works that are based on primary sources.
For example, the presidential papers of Andrew Jackson are a primary source. A twentieth century book about his presidency is a secondary source. Consult your instructor if you are in doubt as to whether you should use primary or secondary sources. Authors' viewpoints will inevitably color their presentation and interpretation of facts. You should be aware of the biases of the author, and not uncritically accept everything he or she says.