If you're not aware of that controversy -- Christopher Columbus didn't discover America, contrary to what's often told -- start at the holiday's Wikipedia page.
If you want something more cerebral, take a look at this "3 things" feature about Columbus from The Washington Post.
And if you prefer watching video instead of reading, this CBS video is worth six minutes of your time. (CBS won't allow me to embed the video here, so you'll actually have to click on the link. Sorry.)
-- Phillip Tutor