PubMed is one of the most used resources when researching medical literature. It's free to use and is managed by the National Center for Biotechnology Information (NCBI) at the U.S. National Library of Medicine (NLM). From the website: 

The PubMed database contains more than 32 million citations and abstracts of biomedical literature. It does not include full text journal articles; however, links to the full text are often present when available from other sources, such as the publisher's website or PubMed Central (PMC).

The NLM offers a free training course to help take the most out of PubMed: Using PubMed in Evidence-Based Practice. Here are the contents:

  • PubMed & Evidence-Based Practice
    • What is Evidence-Based Practice?
    • Using PubMed to Support Evidence-Based Practice
  • Develop a Clinical Question
    • Using PICO to Frame Clinical Questions
    • Using PICO to Identify Search Terms
  • Use PubMed to Find Relevant Articles
    • Perform a PubMed Search
    • Connect Search Terms to MeSH Terms
    • Filter PubMed Search Results
    • Perform a Clinical Queries Search and Filter Results
    • Use the Systematic Review Filter