These databases will generally start you out with a basic one-field search not unlike what you see when you go to Google. Don't fall for it. There are 2 big benefits to database searching: you don't have to scrutinize your results for reliability, and you have the power of the Advanced Search to weed out the irrelevant.
When you're constructing your search, think about how to break your topic down into little bite-sized chunks. You can't just write "Civil War Sherman burns Atlanta" -- well, you could... but it's more effective to break it down, as shown below:
As you add on additional fields for search terms, they'll be joined together by AND by default. This "AND" is the most powerful limiter: the articles you get back have to have term 1 AND term 2 AND term 3 to end up in your results.
If you notice you're getting a lot of articles about Gettysburg instead of Atlanta, you can add another field and switch the AND to a NOT (NOT Gettysburg) to help get rid of those results.
All those terms and phrases and ideas you developed before? They all can feed the Advanced Search machine. Be sure to consider synonyms for your different search terms so you can swap them out to play with your search. (E.g. "college" but also "university" or "higher education")
Plus, because you did that background research, you're starting off with a clearer idea of what information you need to find. This means you'll know what you need to put in those search fields to narrow it down from the massive and generic "Civil War" to "Civil War AND United States AND Sherman AND Atlanta."
Google actually has a number of advanced search options similar to the library databases to help you narrow your results.
For example, to limit your results to .edu, use the "site:" limiter:
You can also use + and -, as well as quotation marks, to control your searches.
|+||Search must contain this word, e.g. Churchill +oration|
|-||Search must omit this word, e.g. Churchill -Jenny|
|" "||Search must find this exact phrase, e.g. Churchill "now this is not the end"|
Note that you can filter your results by publication date by opening up "Tools."
.com is one of the least-controlled domains on the web. (.gov? Only the US government has those. .edu? Mostly universities. .org? Must be an organization, but most anyone can put together an organization.) Before you cite a site, always evaluate it based on the CRAAP test factors.
Look for date of the article (not the overall site's copyright date). Check for an author -- and then look for the author's bio. Who publishes this overall site? Then consider whether there are any citations given for the article's information.