Depending on your assignment, you might need to use a combination of primary and secondary information. What's the difference?
Primary (Think of this as First Hand)
Primary information is comprised of original materials that were created first hand. This type of information is from the time period involved and has not been filtered through interpretation. Examples are:
Secondary (Think of this as Second Hand)
Secondary information is made up of accounts written after the fact with the benefit of hindsight. It is comprised of interpretations and evaluations of primary information. Secondary information is not evidence, but rather commentary on and discussion of evidence. Examples are:
How can you tell the two types of information apart? How would you know when to use one rather than the other?
This clip from the UCSD Social Sciences & Humanities Library will help you understand the two.