Some sources will be focused on well-established facts. These are typically your background information sources. You can paraphrase or summarize these sources as you write your introductory section or at any point where you need to remind readers about the facts of the topic.
Provide context for research
Your research should be built upon the work and ideas of scholars before you. Your paper allows you to share the history, context, and current research on the topic with your reader. These types of sources can be quoted or paraphrased to help you explain why you made certain choices ("We did X in our experiment, as established in the literature") or assumptions ("A study in this source indicated that X is the case. I built on that conclusion by Y).
Support an argument or conclusion
Many times, you are writing from a particular perspective to analyze a concept. As you read, you will find different authors making claims, applying evidence, and drawing conclusions. These arguments or pieces of evidence can be quoted to support your own claims about the topic.
Example: My argument is X. Author 1 also believes X is true as shown in the argument in this source. Author 2 presents evidence to support my argument in this second source.
Provide an argument or conclusion to argue against
You may find that your argument and evidence can be more effective if you have a source to disagree with, and the opportunity to point out where you think they went wrong - maybe they made an error in their data, research method, or assumptions, or you would have used a different methodological approach, or you've identified a potential bias.
It's okay to disagree with scholars, even ones who have had their work published - we are all doing research and we are all scholars. It can feel intimidating to disagree with a published article, but doing so can really help you build a strong paper.
Example 1: Author 1 makes the argument in this source that X is the case. My argument is that while that may be true, Y is actually more important.
Example 2: My analysis of X varied slightly from those reported by Author 1 in this source. Follow-up research should be undertaken in order to determine why this might be.