Primary - In scientific writing, when a scientist describes their own personal work or original research study it is a primary source. Primary sources include research articles, dissertations, technical reports, or conference papers. Primary sources are written for a specific audience (usually other scientists or researchers in the field) and to disseminate research findings that allows other scientists to refute or build upon that work.
Secondary - Secondary sources are articles that critique, discuss, or analyze a study. Overall, secondary sources talk about the research conducted by someone else. Secondary sources include encyclopedias, textbooks, and review articles. One handy trick to tell them apart: since secondary sources are not original research, many, but not all, secondary sources will not have a Methods section.
Hopefully it has become clear why it is preferable to cite primary sources in your scientific paper: if you are referencing a fact or result, you want to refer to the original study that the researcher described in their own words. This helps reduce confusion and mistakes that can result from repeatedly summarizing or paraphrasing a study's result. It also helps to give credit to the original author for their work, and makes it easy for your reader to find the original study you are referencing if they would like to learn more.
However, secondary studies are still useful sources for your research. Secondary sources are especially good resources to direct you to other primary literature and research conducted on your topic. If your professor has not specified which sources you should be looking for, feel free to ask.
Paraphrased from Writing in Biology: A Student Handbook for Writing in Biology, Karen Knisely, 2013, 5th edition, W.H. Freeman and Co
Step One: Write down you research topic or question
Establish what your research topic or research question is. Even a very broad topic gives you a starting point and will help keep you from getting lost and feeling overwhelmed.
Step Two: Read the Abstract
Once you find an article that might relate to your topic, read the abstract! The abstract summarizes the purpose of the article. As you read the abstract, ask yourself: does this relate to your topic or question? If yes, then save the article for later by downloading the PDF, saving it in a citation manager like Zotero, or copying and pasting the citation information in a document. You do not need to read the entire article in that moment. Focus on finding a handful of articles that seem useful.
Step Three: Skim the Article
Once you have an article that you think will be useful, skim it! Read the introduction and the conclusion/discussion sections of the article. While reading, ask yourself: does this article provide you with new information about your topic or question? Does it provide a perspective on your topic you haven't seen before? If yes, then skim the other sections of an article to get a better sense of how this article relates to your topic. If no, then put the article aside. You likely don't need multiple articles that cover the same basic information.
Step Four: Close Read the Article
Once you are sure an article is going to be useful to your research, then take the time to close read the article. Close reading is getting up close and personal with the text. While you're reading, take notes about the article, even if it's just summarizing the content. This will help you engage more fully with the article. The more work you do to identify key ideas or bits of information while reading, the less work you will have to do when it comes time to write your paper.
Helpful note taking styles:
Step Five: Look at the References
While this step could fall anywhere in this list, once you have an article that really fits your topic don't forget to look at the references. The references will identify other articles on the topic and can lead you to other sources for you paper. The author has already done a lot of the work in listing key literature on the topic for you.
Scholarly articles may often seem unapproachable, but they are really organized in a manner to make identifying a useful article easier for researchers. Scholarly articles are very formulaic in their constructions, knowing this formula makes reading them and identifying useful articles easier. Almost all articles are constructed using the following ingredients.