Your answer is partly right but could be better. You said "Wikipedia," which never hurts. But you'll always need a few more sources, whose trustworthiness you can evaluate.
Where else can you get an (accurate) overview about something? You could look at:
- encyclopedias in print (we have over 2,800, in 16 languages including Eskimo)
- encyclopedias online (over 800, including the Guitar Encyclopedia)
- online book chapters from textbooks in fields like medicine or engineering
Or, you could choose a Very Short Introduction. These are those little teeny books you see on the library shelves, about all kinds of things. We have 389 of them.
Here they are sorted by year. The most recent ones are:
- Public Health
- African-American Religion
- American Legal History
Some of my personal favorites are, of course:
The next time you need a short but dependable overview of a topic (Martyrdom? Probability? Sleep?), go to the library catalog, type the phrase "very short introduction" into the TITLE, add one search word, and see what you get.