Reference works, particularly subject encyclopedias and handbooks, are full of overview articles and are perfect starting points for your research. Not only do you get authoritative content, you also get a recommended reading list which will lead you to other high-quality content.
Use this search box to find background information by entering a basic keyword connected with a Boolean search command "AND" to the word "reference" or "encyclopedia."
For example, Type 2 Diabetes AND reference, or Alzheimer's prevention AND encyclopedia
An introduction to using Wikipedia for Academic Research.
Wikipedia should only be used as a preliminary step to better background resources but it can be very useful for locating keywords or key phases, notable researchers or authorities on your topic, and reliable, high-quality resources.