Citation is often approached as an afterthought, something done at the end of the paper solely because the professor requires it. However, citation should be an integral part of the research process. It is designed to help you as well as your readers. Here are some of the ways that happens:
Plagiarism is basically stealing someone else's words or ideas and using them as though they are are your own. Even if this is done unintentionally, it still is plagiarism.
As mentioned to the left, citation helps to show how your paper fits into broader conversations about your topic. With this in mind, consider the conversations you have with friends. You never just repeat what they said. Or when you do, you preface it by saying "So and so said..." The same is true in research and writing. Your thoughts build on other people's thoughts, but you need to acknowledge those links. If you do repeat something, say you did so. Give credit where it is due. To do otherwise is plagiarism.
Plagiarism is just one aspect of broader academic dishonesty, laziness, ignorance, or misunderstanding. A closely related problem is "patch writing," which is much more common. This entails using slightly different language or rearranging words to restate a thought expressed in a sources. Both problems indicate that a student is not thinking or speaking for him or herself. To continue our conversation analogy, consider the fact that when you have something to say, you don't let your friends speak for you. In research and writing, the point is to articulate original thoughts. Other authors cannot and should not write your paper for you. Don't surrend the main thrust of your paper to outside voices.
For those who commit plagiarism, the range or possible consequences is broad. At the professional level, it can lead to loss of job as well as professional humiliation. For students, it can leave a mark on their transcript. However, even if an individual is not caught, there still are consequences. When someone plagiarizes, they don't think independently or critically. They also don't contribute to or learn from the broader conversation in which they could be engaged. Essentially, they lose out on learning the very things they were supposed to learn. Legal repercussions are also a possibility because plagiarism breaks copyright law.
There are also consequences for those who are plagiarized. They lose intellectual control over their own ideas, meaning that they can be misrepresented or superseded in the academic conversations in which they take part. This may hurt their professional or student identities or cost them opportunities for further writing or professional advancement.
Manage your time wisely. Don't leave citation as the last step in an already last-minute paper. Instead, incorporate it into each step of your research and writing. Not only will it mean you have less work at the end, it will keep the rest of the process organized and contribute to your understanding of sources' relationships to each other.
Try putting yourself in your readers' shoes. Would they like to have the option of knowing more about something written in your paper? If so, leave them a citation to use as a starting place. However, if what you wrote is common knowledge so that your reader knows it and will not need to look it up, you do not need to cite it.
Ask your professor or a librarian with help, whether it is trying to figure out how to properly format a source in a citation style or trying to understand how an idea fits into your paper.