Usually one keyword isn't specific enough for your topic.
The boolean operators you need to understand to start out are AND and OR.
In Omni, boolean operators AND, OR, NOT must be in upper case (caps) to be seen as operators rather than search terms. In most other databases, they are not case-sensitive, so it's not necessary to use caps.
Focus your search by adding more search terms and joining them with the word "and".
When you use "and" between terms, you specify that both/all terms must be in every item found.
Using "and" narrows your search. You find fewer items, but they're more specific because they all contain all the key concepts.
Broaden your search by adding more search terms and joining them with the word "or".
Using "or" broadens your search. You find more items, because they only need to contain some of the key concepts.
Be careful of using both AND and OR in the same search request.
To perform a search all in one line, put brackets ( ) around the OR terms.
When you type two words together, a search engine might assume and AND or OR between them:
If you want to keep them as a phrase, quotes are a good idea: "great lakes".
Other search engines may have different rules, and you need to check under "Help" to see how to keep a phrase together.
Not all search engines act exactly the same. Although they are all based on boolean logic and understand boolean operators (AND and OR), they might make certain assumptions.
Better yet, look for an "Advanced Search" option, which helps you organize your search terms by laying it all out for you.
Here's Google's advanced search screen:
See the Omni tutorial for an explanation of Omni's advanced search.