When we research, what are we doing? What are we looking for?
Our goal is to find information to answer our research question. Usually, each resource (article, book chapter, dataset) can answer part of your research question.
We will need to combine information from different resources to fully answer your question.
Example research question:
How does subcontract work affect hospital employees?
I use this research question to find resources. Through doing several searches, I find these resources:
I can combine these different resources to talk about how hospital workers are affected by subcontract work because subcontract work positions make the workers more likely to feel instability, and the workers might then have higher rates of depression. I can also talk about how this might lower the work productivity.
(In a real research project, I should have more than three articles backing my claims.)
A database is searched by creating a search query. A search query is the combination of:
This is an example of a search in Academic Search Complete:

Turn your research question into search terms.
Look at that article's keywords. Keywords are usually written underneath the article's listing in your search results.
Different databases use different keywords. By reusing the keywords, you are learning to speak that database's "language".
Some databases will give you suggestions for search terms when you start typing in a search box. These are terms that the database absolutely recognizes.
Sometimes, the suggestions will be several terms in the same text box, all separated by the Boolean Operator or. This means that the search engine will search for all those terms at once.
Always check before you select a string of terms. Some of the terms might not be equivalent for your specific research topic!