To effectively search any database you should first come up with a list of possible words and phrases related to your research subject, some possible sources to help come up with terms:
Consult what are called, Tertiary Sources.
Encyclopedias and Dictionaries, both general and in your particular subject. Short encyclopedia entries provide a helpful overview of the subject and will often include a list of references and author names that you can pursue further.
These tertiary sources are generally NOT used to support your paper's argument, but they are a good place to start your research journey.
Talk with experts in the field, your professors, colleagues.
Trust your own instincts as a noob subject "expert."
Make a list of possible search terms, keywords, author names to use in searching for resources.
BRAINSTORMING EXAMPLE
Religion and Nature
Possible keywords, concepts, and phrases to use in searching a database on this subject. These and many other terms could be used singly or combined in various ways to conduct a thorough search on the subject.
Religion
Theology
Spirituality
Faith
Sacred
Stewardship
Nature
Environment (-al, -ism)
Creation
Earth
Eco-
Climate
Biodiversity
Related Concepts
Ecotheology
Ecojustice
Deep Ecology
Religious Environmentalism
Eco-Feminism