See the Search Tips handout (pdf) for more information.
Remember: You can use * to truncate, and "quotes" for exact phrase searching; see below for examples.
When searching, group synonymous or similar terms using OR, then combine with other grouped terms using AND.
Searches should be constructed like this:
(termA1 OR termA2 ...) AND (termB1 OR termB2 ...) etc.
If my search topic is, "What are the effects of the armed conflict in Afghanistan on pregnant women and mothers?," I might try a search like this:
(war OR warfare OR "armed conflict") AND (mothers OR maternal OR pregnancy OR "pregnant women") AND afghanistan
See also this Literature Review Workflow, which lists the steps in researching and writing a paper, may help organize your time
What causes disease?
For any "disease" or condition, you could start by considering interactions among environmental and social factors:
Poor diet, resulting from food choices, "causes" nutritional deficiency or obesity in a population.
. . . Keep moving upstream!
Also, consider that how issues are framed is influenced by our assumptions and biases.