Here's a little FAQ video. It's from 2009 but it still counts.
So, Nerdfighters are people who are made of awesome and fight to decrease the level of suck in the world. One of the ways they do that is through the Project for Awesome, held annually since 2007 on December 17th. For more info about P4A go here.
Aside from their main channel, the brothers have several side channels, including: SciShow, where Hank talks about all things science and Crash Course, where John teaches World History, US History and Literature while Hank teaches Biology, Chemistry and Ecology. Hank is also the creator of The Lizzie Bennet Diaries, an adaptation of Pride and Prejudice, and the producer of The Brain Scoop.
The Green brothers have also created DFTBA Records, which is a record label, and VidCon, a conference about online video.
That's all from me for today and remember, DFTBA. =)