Deciding on a topic is possibly the most difficult part of doing research. If you're not sure how to start, talk with your professor, ask a librarian, or...
1. Think about a topic that will keep your interest.
2. Do some background reading from a textbook or subject encyclopedia
3. Narrow your topic to something manageable. You may need to rework it several times as you research.
5. Once you have an idea, write it out as a short sentence or question then pick out search terms.
"How does stress affect memory?" stress, memory