Kindle/Nook - can you explain how it works?

[Midnight Lady]

I asked this in another thread but it got buried, and I am very curious about how these devices work.

In particular, what are the costs involved other than the initial purchase price? How easy is it to find books? Are they expensive? What are the monthly costs for having such a device?

Thanks to anyone who can provide some info on this. I had to give up all my books last year and I have nowhere to store new ones.