PubMed is a United States government National Institute of Health website that provides information about published scientific research. It provides varying amounts of information about the paper depending on its copyright status, but usually provides at least the abstract of the paper, and sometimes the full article. You can easily find PubMed articles by adding "nih" to the end of your google search terms.
Provides full text articles referenced by PubMed.
An abstract is the introductory statement of a scientific study. It describes in broad terms what the study is about, and it's conclusions. For most citizen scientists, without subscriptions to the journals, it is much easier to find and read abstracts than full text of papers. Some medical terminology is used, and you may need to consult other references to unwrap what the abstract is talking about.