Guyatt et al: Users’ Guides to the Medical Literature: A Manual for Evidence-based Clinical Practice (JAMA, 3rd ed. 2015).
The "Evidence Pyramid" is often used to illustrate the development of clinical evidence. As you progress up the pyramid the amount of information available decreases in volume, but increases in relevance to the clinical setting.
Evidence Summaries: aka pre-appraised, filtered, synthesized, summarized. Appraisal is done for you.
Secondary Literature: Publications about primary literature. Appraisal is done for you.
Primary Literature: aka original research, empirical research (based on observation or experience). YOU must appraise.
The Cochrane Collaboration is a global independent network that summarizes the best treatment evidence through high-quality systematic reviews and other synthesized research evidence to inform health decision making.
The Cochrane Database of Systematic Reviews (CDSR) is the official journal and database for Cochrane Reviews and protocols, and is accessible through the Cochrane Library.
Cochrane reviews are indexed in PubMed, CINAHL, Embase, and Web of Science.