PubMed User GuideNCBI's comprehensive help manual
PubMed Online TrainingIncludes handouts, quick interactive tutorials, and online classes
PubMed EssentialsOn-demand PubMed course developed by the National Network of Libraries of Medicine
MEDLINE/PubMed Resource GuideA list of links to information and training resources from NLM
What is PubMed?
PubMed is a database of over 30 million biomedical article citations maintained by the National Library of Medicine.
MEDLINE is the largest subset of PubMed, containing over 27 million citations which have been indexed by the National Library of Medicine and have had Medical Subject Headings (MeSH) terms applied.
PubMed Central (PMC) a separate database of 5.3 million citations composed of citations (and usually full text) for articles which are free and can be accessed by anyone (i.e. not restricted by a publisher pay-wall). PMC content is searchable in PubMed.
It is important to note that PubMed is a citation database, not a full text database, so when searching PubMed, you are searching the citation information contained in these fields only, not the entire text of the article.
For more information, see:
What is in PubMed?An interactive tutorial from the National Library of Medicine covering what you can find in PubMed & how it got there
MEDLINE, PubMed, and PMC: How are they different?A fact sheet by the National Library of Medicine