PubMed is one of the most-used and respected biomedical databases that encompasses many medical topics: biology, medicine, health, psychology, nursing, rehabilitation, veterinary sciences, etc. PubMed is also VERY powerful and offers a lot of nifty tools.
MeSH is the National Library of Medicine's controlled vocabulary. This means that every record that is in PubMed will be assigned MeSH terms (cateogories) as a way to organize them and make articles, eBooks, etc. easier to find. MeSH terms do some work for you because they associate groups of similar concepts together.
For example, if one of your search terms is "Patient Education" then you should search "Patient Education" in the MeSH database to see how PubMed will interpret your term. Not everyone uses the same definitions and the same context, so understanding how your words will be searched gives you a better understanding of what your results may be.
When I search "Patient Education" in MeSH, this is what I get:
I likely need the first result, "Patient Education as Topic".
You will get several MeSH term results if what you typed in relates to a couple option. The first term refers to the "teaching or training of patients.." the second refers to the actual handout or publication type used for patient education. Which do you mean?
Details on the MeSH Term: Patient Education as Topic
Here I can see how PubMed defines the term, what subheadings can be used to narrow your search, the entry terms (concepts automatically included with the MeSH term), and MeSH tree.
The MeSH trees give me an idea of how this concept related to broader or more narrow terms.