The basic Google search assumes AND between each word.
For example, medical science breakthroughs will find sites with all three words. Use OR if you want either of two terms e.g., medical science breakthroughs OR discoveries.
To better focus your search:
- Use quotes to search words as a phrase, e.g., "breast cancer"
- Use minus sign to eliminate undesirable words, e.g., viruses -computer
- The minus sign seems to be variably supported at this point (2021)
Search specific sections of sites for better precision:
- Use site to find certain types of sites, e.g., site: gov or site: edu
- If you want to use gov, org, edu all at once you can write it (site:gov OR site:edu OR site: org)
- Use filetype to find specific formats, e.g., filtetype: ppt or filetype: doc
- Use intitle to find sites where words are in title of the page, e.g., intitle: google search tips
- Use inurl to find sites where a word is in the URL, e.g., inurl:ucsf library leads to site with both words in URL
- Use link to find pages linked to the one in questions, e.g., link:www.library.ucsf.edu
Sadly, Google has retired the tilde (~) for synonym searching and the plus sign (+) to insure a word is included in your search.