Figuring out what to search to find the information you need can be challenging. That is why the card catalog and databases offer so many different ways to search.
Keyword search -- uses a word or words that describe your subject to find it
Subject search -- uses pre-established subjects (that you have to know or guess) to search for the information you need.
Natural Language search -- allows you to search in the way you speak, with the search weeding out the words it doesn't need to find the information
Using a natural language or keyword search will often lead you to the subject assigned to your topic, which will expand your access to resources that will assist.