I thought Pottermore

Was just a website where you could read Harry Potter. Am I wrong?

You should read the video of J.K. Rowling on the Pottermore site to help you, I think that'd give you the best understanding. In the "Help" section there was something about this, although, I can't find it now.

No one really knows yet. It has something to do with background info though.

Well, though we don't know fully all about it we know some of the things Pottermore has to offer considering what's talk about it online, and JK Rowling's video. It's supposed to enhance the reader's experience and to bring "Harry Potter storylines to interactive life for readers" when they're reading Harry Potter, and to discover "behind-the-scenes" information and previously unpublished material about the world of Harry Potter; extra details etc.

The members can also post their own comments, drawings etc and it's designed as a "place to share the stories with your friends". It'll also offer eBooks, like you said, not sure if they're free or not, but I heard others saying they were while you had to pay for them. I'd imagine you'd have to pay, of course.

It's really interactive, you can play games and take a quiz for the house you're in - I hope I'm not bias, since I've read the books, I might know which answer is for which house, for the values and how one would act. You can also choose your wands, go to Diagon Alley, etc. Then after you're sorted into a house you go to the common room and "explore".

So to ask if Pottermore is just a website to read Harry Potter books was an understatement. I think it'd be most wise if you went to the site and watched the video and research online. Might give you a better understanding.