Step 1: Think about your topic! What questions are you trying to answer?
Step 2: List terms that best represent the main concepts of your topic.
For example:
If nothing comes to mind, it is time to do some background research!
Start with MedlinePlus, by the National Library of Medicine, for a general introduction to many medical topics, often written in a consumer-friendly language. It includes an online medical dictionary, an illustrated encyclopedia, and drug information.