Truncation is a way of giving your search tool flexibility to find alternate endings for your search term.
Why it's helpful: Search engines match your terms to results; they will not find an alternate version of your term. Truncation tells the search to match the root of your term and gives it freedom to find whatever endings it can.
How to do it: Shorten your search term to its base or root form. Then add a truncation symbol to the end of your term. Note: truncation symbols vary by search tool.
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