Sources can play several different roles as you develop your points:
Provide background information or context -- You can use facts and statistics to support generalizations or to establish the importance of your topic.
Explain terms or concepts -- Explain words, phrases, or ideas that might be unfamiliar to your readers. Quoting or paraphrasing a source can help you define terms and concepts in neutral, accessible language.
Support your claims -- Back up your assertions with facts, examples, and other evidence from your research.
Lend authority to your argument -- Expert opinion can give weight to your argument. But don't rely on experts to make your argument for you. Construct your argument in your own words and cite authorities in the field for support.
Anticipate and counter objections -- Do not ignore sources that seem to contradict your position or that offer arguments different from your own. Instead, use them to give voice to opposing points of view before you counter them.