As an author I don’t know what I’d do without Wikipedia. It is the first place I go when I want to get a fundamental and easy to understand glimpse at something. If I need to do more research, I do, but more often than not I find everything I need for the purposes of a novel right there. If you haven’t used them, you should try them.
They are a nonprofit who relies on donations and hopes to keep it ad-free. If you use them, I encourage you to donate. They are a tremendous resource and it’s beyond refreshing to be free of ads distracting your attention.