PubMed is made up of several parts, including Medline, some other life science journals and books, and some proceedings and reports. It can be searched using key words and/or Medical Subject Headings(MeSH).

For a comprehensive search: If you are trying to make a comprehensive search, or your topic is very new to the discipline, combining key word searches with MeSH terms may be your best strategy. Not everything in PubMed has MeSH terms attached or associated and terminology and vocabulary can vary. PubMed's Entry Terms, which are phrases or words that have been commonly used to search for a topic successfully were developed from analysis of past search histories, and they guide us to content by retrieving the associated citations labeled with the Entry Terms and some that are also labeled with the relevant MeSH terms- and you can look at the MeSH terms at the side of the citations to explore what they are. 

For precision: MeSH headings or MeSH terms increase the precision of searches, so if it's vital to have very specific and more easily replicable searches, MeSH terms may be crucial. They help disambiguate terms, such as the word expression*, which can indicate facial expression, gene expression, or the process of squeezing juice from an orange. Using gene expression[MeSH Major Topic] yields only the citations that are specifically looking at that kind of expression, as does "Facial Expression"[Majr]  for that topic. 

*example drawn from the John B. Coleman Library's guide about MeSH searching. https://pvamu.libguides.com/c.php?g=996498&p=7211976

Note: All of the content in Medline and some content in PubMed is labeled with MeSH terms. The terms are hierarchical, which means that the MeSH terms in the 'tree' are modified by subheadings to make them gradually more specific. Each MeSH tree has sixteen (16) possible branches. Again, the MeSH terms can allow you to develop a very specific search as you select MeSH and subheadings that work. 

Looking at it a different way, you could search using the word taste, or, if you were checking the listing of MeSH terms, the word taste shows up in several ways: You could click the check boxes beside the most relevant terms to include those terms in your search. 

• Boolean operators: PubMed acts as if there are ANDs between terms. But you may still use AND, OR and NOT to make the search work as you wish:
  • Boolean operators  (AND, OR, NOT) MUST be entered in capital letters to be recognized as operators.
    • OR—use OR between similar keywords, like synonyms, acronyms, and variations in spelling within the same idea or concept. OR gets more results. Put your search in parentheses if you are using OR, to get it to work properly.
      • For example: (myocardial infarction OR cardiac arrest)
    • AND—use AND to link ideas and concepts when you want both ideas or concepts in your search results
      • osteoarthritis AND (swiimming OR bicycling)
    • NOT—use to exclude keywords from the search. Use NOT sparingly because you may knock out something important.
      • treatments NOT weight loss

• Truncation: To search for all terms that begin with a word, enter the word or word stem followed by an asterisk (*). 

  • Enclose the phrase in double quotes: "breast feed*"

  • Use a search tag: breast feed*[tiab]

  • Use a hyphen: breast-feed* 

    • At least four characters must be provided in the truncated term, and the truncated term must be the last word in the phrase.

  • NOTE: Truncation turns off automatic term mapping/the use of entry terms and the process that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy. For example, heart attack* will not map to the MeSH term Myocardial Infarction or include any of the more specific terms, e.g., Myocardial Stunning; Shock, Cardiogenic.

• Known article: For a known article, you can put in an author's name, the year of publication, and a word or words in the journal title into the ALL FIELDs search and often retrieve a specific citation. For example: Fauci AIDS 2018

• Proximity searching lets you look for multiple terms appearing in any order within a specified distance of one another, but ONLY in the Title or the Title/Abstract fields.
  • 1. Select your search terms (two or more); put them in "quotation marks"
  • 2. Decide the best spacing; how many words can the search terms be separated by and still be useful?
  • 3. Set up your search like this:
    • "search terms" [field name or field code: ~N], where N is the maximum number of words that your search terms can be apart.
      • "mitral regurgitation" [Title/Abstract: ~2]
      • "rational healthcare"[tiab:~1]
      • "hip pain"[Title: ~4] AND stretching
• Advanced Search screens and features are provided both for general searching and for searching within the MeSH hierarchy. 
• There are LOTS of short tutorials about how to use PubMed, made by the developers and staff of the National Library of Medicine.

https://www.nlm.nih.gov/oet/ed/pubmed/nlm-office-hours_proximity_searching.html#:~:text=Proximity%20searching%20in%20PubMed%20allows,or%20the%20Title%2FAbstract%20fields.

1) Enter the author’s last name and initials without punctuation in the search box, and click Search. 

2) Enter the author’s last name, and use the author search field tag [au], e.g., brody[au]. and click Search. 

Names entered using either the lastname+initials format (e.g., smith ja) or the full name format (john a smith) and no search tag are searched as authors as well as collaborators, if they exist in PubMed.

3) Enter a full author name in natural or inverted order, e.g., julia s wong or wong julia s. and click Search. More information means fewer results but usually more accurate retrieval. 

You may also enter an author search with other search terms, such as Douda AND Crispr in the "All Fields" search. This will retrieve articles with Douda as an author or from cited references, and Crispr wherever it occurs. You will get closer and fewer results if you did the same search with Douda in the author field and Crispr in the title field or title/abstract field.

PubMed has an advanced search page, which allows you to search using an array of modifiers, from MeSH to authors' names, to publication titles to grant numbers or volume numbers. Open the Advanced Search by clicking on the Advanced Search option below the general search bar. 

They call it the Advanced Search Builder because you add the terms as you go, and then they are compiled into a search statement. The marked dropdown menu, circled below, allows you to choose from many options, including Affiliation. If you want to search for information in several specific fields, like Author and Publication title, you will need to change the search fields as you go. All Fields is the broadest search, and also where you can combine an author's name, a distinctive word or words from a title, and a year to draw up the related citation if it is in PubMed; for example: Doudna Crispr 2017

1. Identify the key concepts for your search. 
2. Enter the terms (or key concepts) in the search box.
3. Press the Enter key or click Search.

For many searches, it is not necessary to use special tags or syntax. PubMed uses multiple tools to help you find relevant results:

• Best Match sort order uses a state-of-the-art machine learning algorithm to place the most relevant citations at the top of your results.
• An autocomplete feature displays suggestions as you type your search terms. This feature is based on PubMed query log analysis described in " Finding Query Suggestions for PubMed ."
• A spell checking feature suggests alternative spellings for search terms that may include misspellings.
• A citation sensor displays suggested results for searches that include terms characteristic of citation searching, e.g., author names, journal titles, publication dates, and article titles.