Jimmy Wales founded Wikipedia. You have used it before because it's a helpful tool to learn and if you've learned anything in the past several years your quest for knowledge likely led you through Wikipedia at some point.
Jimmy Wales doesn't like SOPA and, even though that Internet-censoring law has been shelved for the time being, he has not forgotten the threat of what a SOPA can do. To emphasize how SOPA will screw up all of the Internet for all of the people, Jimmy Wales has decided to do something:
The 24-hour blackout will affect only the English-language portion of the site, but lots of people speak English and so you can expect that lots of people will feel the effects of such a gap in the Internet. However, Wales says that Germans will run a banner about the SOPA-protesting blackout and other language versions will be able to make their own decisions about the site.
And yes, though SOPA may be on hiatus at the moment but, just like comic book villains and the moldy sour cream you unknowingly ate with your burrito at lunch, it is likely to come back and haunt you. Besides, PIPA, the Senate's quiet yet equally evil step-sister to SOPA, is still haunting Congress and the Internet. So come Wednesday, January 18th, you will not Wikipedia anything so as to show you how hard it is to do school reports or learn anything without the enormous resource that is Wikipedia. Go ahead and preview it now: Google something. Anything. I bet you the first result is a link to that term/object/concept's Wikipedia page.
And that should give you a pretty good idea of how cemented Wikipedia is into our info-searching habits. Good luck finding a better starting point in your search inquiries.