Whether you're an expert when it comes to history, grammar, or obscure murder cases, you (yes, you!) can become a Wikipedia editor — and it doesn't even require registration. Anyone can start, and you'll be helping Wikipedia continue to be the endless wealth of information (and BONKERS STORIES) that it is.
To get started, take a look at Wikipedia's Help:Editing page. It tells you how to make edits, what kind of tone to use, how to add references, and more. Peruse some Wikipedia pages you find fascinating, and when you find changes to make or have an interesting addition, you can get going and submit edit requests.
For more info, check out Wikipedia's guide on editing for the first time.