Watch the tutorial below for a demonstration on creating a basic topic search in PubMed.
Take a look at the captions in the image below to understand the components of a PubMed citation entry.
What are MeSH terms? 
MeSH stands for Medical Subject Headings. These are the standard terms added by indexers to the article record to help improve search results.
National Library of Medicine indexers examine articles and assign the most specific MeSH headings that describe the concepts discussed.
The indexer assigns as many MeSH headings as appropriate to cover the topics of the article (generally 5 to 15). When there is no specific heading for a concept, the indexer will use the closest, general heading available.
Indexers can also assign Subheadings to further describe a particular aspect of a MeSH concept. Examples of Subheadings in this list are: therapeutic use, physiology, surgery, drug therapy.
Why are they important?
Because they are a controlled vocabulary used by the National Library of Medicine, using them can expand your search results and help connect you to all of the articles on your subject. You can search for your topic in the MeSH database to find the MeSH terms that represent your subject.