you can get books onto the kindle in one of two ways. If you have wireless internet, or go to a wireless hotspot you buy the books off amazon and it automatically downloads onto the kindle without you having to use the laptop (£109 version) or just browse from the kindle and download. If you get the 3G £149 version you can download books anywhere at anytime straight from the kindle store via the kindle.
depending on what books you like, there are a fair few books available free on amazon, or for a very small charge. I find that amazon's special offer type books are usually cheaper to buy in book form rather than kindle (for example i went on yesterday because dawn french's book is on special offer but it's significantly more expensive as a kindle download)
Personally i love my kindle, and it was a god send when i was in hospital. However, you have to remember that any books you download, are never "yours" if amazon decided to withdraw permission for you to read them on the kindle, they would just take them back (not that thety ever would as it would be a complete marketing disaster)