The exponential growth of currently available evidence has made it necessary to collect, filter, critically appraise, and synthesize biomedical information to keep up to date. In this sense, systematic reviews are a helpful tool and can be reliable sources to assist in evidence-based decision-making. Systematic reviews are defined as secondary research or syntheses of evidence focused on a specific question that -- based on a structured methodology -- make it possible to identify, select, critically appraise, and summarize findings from relevant studies. Systematic reviews have several potential advantages, such as minimizing biases or obtaining more accurate results. The reliability of the evidence presented in systematic reviews is determined, amongst other factors, by the quality of their methodology and the included studies. To conduct a systematic review, a series of steps must be followed: the formulation of a research question using the participants, interventions, comparisons, outcomes (PICO) format; an exhaustive literature search; the selection of relevant studies; the critical appraisal of the data obtained from the included studies; the synthesis of results, often using statistical methods (meta-analysis); and finally, estimating the certainty of the evidence for each outcome. In this methodological note, we will define the basic concepts of systematic reviews, their methods, and their limitations.