By the time a person gets into college they should know how to write a good research paper. If not, then they are going to be in a world of hurt when they get there. Research papers tend to be popular assignments when dealing with college professors.
When you are researching your paper there will be some sources that are used more than others. If you are making citations as the research progresses then you should be able to easily discern which ones those are. If you are not citing them as you go then you are just making things harder for yourself in the end.
Anyway, back to the point at hand.
Your primary source will by definition be the one that you get the most information supporting your topic from. This could be a book, a web site (that is, a qualified true and unbiased site…usually these will be those with addresses ending in .edu or .gov), a person who you may have interviewed or even a documentary or newspaper. Whatever your primary source is, because of the amount of information you get from it this should be the heart of your paper.
Your secondary source will be the one that you got the next largest amount of information from. All of this information should be supporting the information from the primary source. This information can come from the same sort of outlets as the primary source but be of a different type. In other words both your primary and secondary sources should not be the same book.
All in all when you are writing any type of paper there will generally be more than one type of resource used. Use your judgment and find sources that will support the theory that you are putting forth. At the same time remembering to throw in a few sources that go against your theory will add the element of you theory being able to be defended against these other theories. Your instructors will find a paper written like that more engaging and may inspire a better grade.
Always remember to cite each and every source that you use…not just the primary and secondary ones. Failure to cite references can lead to criminal charges of plagiarism as well as expulsion from school. It only takes a few minutes and will save you a lifetime of regret in the end.