The Cochrane Handbook defines synthesis as "a process of bringing together data from a set of included studies with the aim of drawing conclusions about a body of evidence" (Section 9.1). Usually this process starts with an examination of the included studies following the PICO framework (or other question framework). You might outline the characteristics of the studies' interventions, populations, settings, outcome assessments used, etc. You might visualize the results of this synthesis via one or more tables.
Sometimes statistical analysis is impossible or outside of the scope of the intended project. For example, scoping reviews should be used to map the current state of research on a topic, summarize and disseminate research findings, or identify research gaps. Therefore statistical analysis would be inappropriate in a scoping review. Instead, these reviews may engage in narrative synthesis.
The Synthesis Without Meta-analysis (SWiM) guideline is a nine item checklist to promote transparent reporting for reviews of interventions that use alternative synthesis methods. It is intended to complement, not replace, the PRISMA guidelines. Find more information on the SWiM website.
Many systematic reviews use some sort of statistical synthesis to analyze the data. One popular method is meta-analysis, which can be defined as "the statistical combination of results from two or more separate studies" (Cochrane Handbook, Section 10). But meta-analysis isn't always possible. Refer to the Cochrane Handbook for a list of additional statistical synthesis method, along with the types of questions they best address and examples (Section 9.5).
The SJSU Library does not currently have the capacity to advise on data analysis, including statistical synthesis methods. Instead, your librarian would be happy to help you identify resources and tools which could help you learn how to do your own analysis. You might also consider reaching out to colleagues in other departments on campus who might be interested in interdisciplinary collaboration.