Select the most important 2-3 terms related to your topic. Put the word AND between each new term; this tells the database to look for resources with ALL your terms.
global warming AND atmosphere
Use quotation marks ( " " ) around phrases (two or more words); this tells the database to look for the words in that specific order.
"climate change" AND atmosphere
Use an asterisk (*) to find multiple endings of one word. Using pollut* as a search term will include results that refer to pollute, pollutes, polluted, polluting, and pollution.