Truncation works best when you are searching for different aspects of a topic. Let's use Academic Search Complete for this example, as it's a good general database. (When you're ready to get more subject-specific databases, try our Subject Guides).
For example, if you were looking for research on drunk drivers, you might type "drunk drivers" into the search box. (Use quotes to filter out results with only one word or the other in them).
If you shorten drivers to driv* and add an asterisk, you will pull in results with the words "drunk driving" and "drunk drivers". You can also limit your search by changing the drop down box options from Select A Field to Subject Terms, Title, Author, Journal Name and other options.
This should work for most EBSCO databases (you can find out if you're using an EBSCO database by checking out the logo in the upper right hand corner). Other databases may require a $ or other symbol in place of the asterisk. You can find out by checking the Help section.