If you are writing a research paper for a class, consider the other students. Is it likely that they will also be writing about your topic? How can you keep your paper unique and interesting if everyone is writing about the same thing?
To draw a parallel, a lawyer researches and reads about many cases and uses them to support their own case. A scientist reads many case studies to support an idea about a scientific principle. In the same way, a history student writing about the Vietnam War might read newspaper articles and books and interview veterans to develop and/or confirm a viewpoint and support it with evidence.
Once you’ve gathered all your research, print it out (if it is an online source) and gather post-its or anything you need to mark notes in the books/magazines you are using. This step is very important: read through your research, take notes on what you think is important, and highlight key facts and phrases. Write directly on copies you’ve made, or use slips of paper tucked into pages to mark places of importance.
If you find one really awesome book or journal that fits your topic perfectly, try looking in the works cited/bibliography/reference list at the end of it. This should contain many more books and journals that are about your topic as well.