Experimental or observational, case-control and cohort study, analytical and descriptive, randomised and non-randomised, outcome-exposure or exposure-outcome, risk of bias. Understanding how to read a research paper or start a research project is challenging and an important skill in nursing. Have a read of this article to help understand clinical research:
Grimes, D. A., & Schulz, K. F. (2002). An overview of clinical research: the lay of the land. The Lancet, 359(9300), 57-61.
And this Introduction to Study Design by Jeremy Howick

Additional Resources
Greenhalgh, T. & BMJ Resources. How to read a paper.
Howick. J. (2013). Introduction to Study Design.
Nursing Education Network. (2018). Barriers to using research findings in practice: The clinician’s perspective.
Nursing Education Network. (2018). Nursing Research Process a Quick Guide.