If you are writing for an academic, scientific or professional audience, citing your resources is mandatory. Breaking this rule in these institutions can not only be embarrassing, but it can have negative consequences. If you're writing for a consumer publication, such as a magazine, editors don't want compositions that are filled with citations or quotations, so you may only need to provide them as references.
YourDictionary.com defines research as "careful, systematic, patient study and investigation in some field of knowledge, undertaken to discover or establish facts or principles." Research is needed in writing to gain the information necessary to compose and support an article.
Plagiarism is when you present another person's ideas without giving them credit. Within this general rule, there are different levels of plagiarism. The worst offense is the straight copying of someone else's words and presenting them as your own. On the other end of the spectrum, you might simply present someone else's idea in your own words. It is always better to provide all your sources for an article.
It is important to learn when you need to cite a source and when it is all right to put it in your own words. If the material is common knowledge, you do not need to cite it. However, if you quote the exact words, it should be cited. Facts and statistics also should be cited, especially if they are different from what is commonly known. If reading your paper is similar to reading the original article, then you have plagiarized. If you have presented an idea as your own that isn't, you have plagiarized. The same is true if you have used someone else's image or other production without acknowledging the source. Learning the rules about when and how to cite correctly narrows the gray zone -- the place where you wonder: Am I plagiarizing? -- that writers fear they might cross.