You will need to think of words to search for in the databases so the database can give you good results. The database will return results that match what you tell it to find.
Break down the parts of your topic and identify the most important ones. Then determine what the databases might call these topics. For example:
What is the effect of stereotypes on treatment for mental illness?
Stereotypes = stereotype, stereotypical, cliches, myths, gender, race, etc.
Mental illness = "mental health," depression, schizophrenia, etc.
Treatment = therapy, medication, loxapine etc.
A search might be:
(stereotyp* OR cliche*) AND "mental illness" AND therap*