Using databases can be quite different than using Google. While Google is designed to respond to the natural way people talk (i.e. complete sentences), databases require you to break your subject down into keywords.
For example, if you typed "how does heavy metal pollution effect the health of homeless populations?" into a database, it's going to search for instances of all those words, including the irrelevant ones (how, does, the). You're really only interested in articles that mention the following words or concepts:
These are going to serve as your initial set of keywords (also known as search terms).
If you just use these terms to start, you have a pretty good chance of getting relevant results. However, it may be helpful to organize your search terms in a thoughtful way. You may also find that there are other words you can use (like "unhoused" for "homeless" or "breathing quality" for health). This is where Boolean operators come in.
Boolean Operators are three different words -- AND, OR, NOT -- that you can use to organize your keywords:
Let's say you're researching the current challenges of salmon management.
If you search for "salmon management" AND challenges, you will only get results that mention BOTH words. This will get you less results but they will be more relevant than if you just search for "salmon management."
On the other hand, let's say you're not getting enough results. Maybe the scientific literature uses a different word, or maybe there are more than one way to say what you are looking for.
Going back to our original example, fisheries are another word we could use for "salmon management," so if we combine them using OR like this:
we will get more results that if we just used "salmon management" because the database knows to give results that include EITHER word.
Thus, the OR operator can be used to connect similar words or synonyms together. This is especially useful in the sciences as many species of animals have scientific (or Latin) names. Including the common and Latin name using OR will get you more relevant results.
The NOT operator is a little tricky to use. You'll only want to use it if unrelated words or concepts keep showing up in your searches. For example, "heavy metals" contribute to pollution but that term is also the name of a musical genre. If you use the NOT operator like this:
you will eliminate any results that are related to music.
Be careful with the NOT operator, though. You could unintentionally eliminate relevant results if the excluded term is still somewhat related to your search!