This site made available by NCBI PubMed is a specialized search tool that can be used to design and implement selective, information field-driven text searches for publications and/or published scientific data linked to publications or cited references.
April 30th, 2020: As of this date, the page "Frequently asked questions" link is not navigating properly, generating an informed error upon link activation ("Error ID # [4a1b99ab-f8d0-41bb-acf6-6e022803c760]"). The PubMed website in entirety has been undergoing a redesign from 2019 into 2020. The new site will become the default mid-May, as per an announcement posted to the site (see link).
This video below demonstrates how to use the PubMed Advanced Search Builder; a good way to refine PubMed searches.