Answer
In general, searching in a database is best accomplished by using keywords, subject headings, or groups of terms.
However, sometimes it's better to use phrases. To tell a database to search for a specific phrase: type quotation marks (" ") around the phrase that you need to find. This will tell the database (or search engine -- this works in Google, too!) that you want it to find the words you typed exactly as you've typed them. Using quotations will provide you with a more narrowed search.
For example, compare these Summon searches:
Without quotation marks: severe physical disabilities = 272,764 results
With quotation marks: "severe physical disabilities" = 5,325 results