You want to use specific keywords that represent the main concepts of your topic, rather than typing in a whole sentence. Start with your topic statement or question and underline the main concepts.

Topic: Do electric cars help air quality?

Find alternate terms in case the first terms used do not turn up the desired results.

Electric cars:
electric vehicles

Air quality:
air pollution
smog
greenhouse-gas emissions

Once you start searching, you will hopefully find some sources that are relevant to your topic. Look in the details section of those sources to find subject terms. These will provide good alternate terms for your searching.

Image of subject terms from source found in search; can be used for keywords

Also notice terms used in reading these sources that may help you search and further define your topic.