Think about it: search engines crawl thousands, maybe even millions and billions, of pages or records trying to match your search term with results. You're going to be absolutely overwhelmed with results if you only enter a single search term. You're also going to find a lot of completely irrelevant stuff.
So how can you improve your chances?
Come up with multiple search terms and combine them using the options described here.
Combining search terms with AND will:
Search for politics = 296 million results
Search for "college student" AND politics = 43 million results more focused on your topic
Search for "college student" AND politics AND "2008 election" = 543,000 more relevant results
Search for Adam Smith = 38,700,000 results
Search for "Adam Smith" = 2,730,000 results
Search for theory of relativity = 3,430,000 results
Search for "theory of relativity" = 856,000 results
Backwards Reference Searching
What it yields:
It looks into the sources that your author referenced. This means the sources have already been vetted by your author for credibility, and you know that they are related to the topic at hand. However, it also means that the sources must have been published before your original source, so you will be retrieving older materials.
How to do it:
Tools to use: