Primary vs. Secondary?
Primary - In scientific writing, a primary source is the original research study. Primary sources more often describe the research in detail and has not been filtered through evaluation by others.
Secondary - Secondary sources are articles that critique, discuss, or analyze a study. Overall, secondary sources talk about the research conducted by someone else.
If your professor has not specified which sources you should be looking for, feel free to ask.
To help identify the parts of a scholarly article, check out this interactive tutorial created by Andreas Orphanides at NCSU Libraries.