When you search a web tool like Google, you are searching every word of every page of every document, from beginning to end. There are no rules about what goes into Google, so you get a mix of everything. And, Google can't always tell the difference between a page or article that is all about your topic, and a page or article that mentions your topic only once or twice.
When you search in the library research tools, like the catalog or (most) research databases, you are actually just searching short "profiles" of the book, article, or other source that you are looking at, rather than the whole source. Because the profiles are very short, searching for entire sentences or phrases does not usually work well in library resources.
But, if a source comes up because its profile mentions your topic, it's much more likely that the source will actually be on your topic. And while the research tools have many different types of sources in them, they're all published sources, so they've been checked for quality on at least a very basic level.
When you're using databases, you want to use keywords to search for materials related to your topic. Lets say your project is about the book Sula by Toni Morrison. Here are examples of key words I might use to find results:
Sula, Toni Morrison, black women, feminism, literature, black feminism, character analysis
You can search for these terms individually or try combining them for more refined results. Try using search terms like AND, OR or NOT.
If I use the terms "Sula" and "black Feminism" and "feminism" I will get results that contain all of those search terms together.
Sula and ("black feminism" OR feminism) will bring up results that include clybourne park as well as either review or critcism or both words together.
Use NOT when you want to exclude a word or phrase.
Here are some general tips to guide you in choosing your search terms:
Bonus Tip:
When you find a good article, look at its References or Works Cited list. That will often lead you to other useful sources. You can also look at information such as the name of the journal or the author for ideas of other ways to search.