Michael Schwartz Library
Google doesn't make public the algorithms they use to index and rank their results, but their website tells us this much:
"Google Scholar aims to rank documents the way researchers do, weighing the full text of each document, where it was published, who it was written by, as well as how often and how recently it has been cited in other scholarly literature."
Keep in mind that it's important for you as the researcher to evaluate the results of a Google Scholar search carefully to find the highest quality content for your research.
According to Google's website, the purpose of Google Scholar is to allow you to:
Strengths of Google Scholar
Weaknesses of Google Scholar