Research in the sciences is founded on interpretation of data, from experiments and observations. You identify a specific question or topic, and you determine what supportive evidence is needed. The question you've identified is not the first on the topic; other researchers have written about it as well. The experiments you design, the observations you make, and your interpretations of all that data are part of an extensive conversation with researchers in the past and across continents, and they open up new questions for future researchers.
Scientific research of course relies on experimentation and observation, but it also requires a knowledge of the conversation that you're entering. Only by acknowledging interpretations that already exist can you present your field with something new. To find these materials, you'll need to find scholarly sources. Your research design may be identical to something that's already been done, but your interpretation of the data (or even the results) may be different. Or, you may create a completely different design to respond to the same question, as a way to find different or more significant results. But only by finding research that already exists can you expand the field.
Original research refers to scholarship written to expand a field of knowledge. It usually involves experiments and observation, answering a question not addressed in the field. Sometimes referred to as primary resources, original research is the first place the study has been discussed.
Review Articles are discussions of the state of the field at the time the review was written. For example, climate change scientists in 2017 want to know about studies of sea ice in the past twenty years, so they can avoid duplicating studies, and so they can position their own work to make a meaningful contribution to climate science. Review articles discuss many different studies, explaining how the field has changed, what areas the field has addressed thoroughly, and what areas of study are still missing.