Typically, you would begin with a question or general topic and look to refine results until you found a specific item you're interested in, though this assignment runs a little backwards, beginning with a very specific article you then need to find. To get relevant results, you'll need to identify keywords to search. You can do this by evaluating which words are associated most closely with your topic and are unlikely to appear in the same combinations referring to other topics.
Here is an example blurb from the April issue of Monitor on Psychology:
People who work too much are twice
as likely to become depressed, finds a
study led by a researcher at the Finnish
Institute of Occupational Health. The
authors followed more than 2,000
middle-aged British workers over the
course of five years and found that those
working 11 or more hours a day had
nearly double the odds of experiencing
a major depressive episode than their
colleagues. (PLoS ONE, Jan. 25)
Identify the major ideas in the text:
People who work too much are twice
as likely to become depressed, finds a
study led by a researcher at the Finnish
Institute of Occupational Health. The
authors followed more than 2,000
middle-aged British workers over the
course of five years and found that those
working 11 or more hours a day had
nearly double the odds of experiencing
a major depressive episode than their
colleagues. (PLoS ONE, Jan. 25)
The highlighted words were chosen because they seem to be at the heart of the content, and all of them put together seem likely to summon this particular article. Of those, the main terms would probably be work and depression. Throw those into Digger Search and sure enough, this article is the 9th listed result. In this case, those keywords were just accurate enough to return the desired item. Suppose, though, that you were looking for something that returned many more results, all of which used the words work and depression. Even if the item you're looking for was among the most relevant 2% of results, with thousands of hits it might still get pushed back to the third or fourth page. As a result you may not see it, or give up before you get to the correct page.
Going back to our highlighted words, we can pick out slightly more specific terms and add them to our search. Perhaps a lot of items used the word depression, as that's a common word used in many contexts--you could imagine the words work and depression appearing in an article about the economic impact of the Great Depression, for instance. It's much less likely that such an article would use the term depressive episode.
In Digger Search, submitting the search work depressive episode brings the relevant study up to the number one result.
A lot of successful searching does boil down to trying different combinations of keywords, and even subtly changing the words themselves. In this case, changing from depression to depressive improved results, because it made it that much more likely that a result with that term would be the specific item we're looking for.