I just got a Nook WiFi and I am looking for other places to download books.?

I just got a Nook WiFi and I am looking for somewhere else to download books. I read books like Twilight, House of Night, and I want to read Sookie Stackhouse, Hunger Games, and other books like them. I am not very computer smart so Im not sure what I am looking for. I would like cheap or free books. Could you please help!!!!