You get the photo taken and have your magic band scanned. If you do not have a magic band I believe the photographer will provide you a card with a code on the back. You can get one with the first photo you have taken and keep using it the entire trip.
The photos will appear on the Photopass area of your My Disney Experience account
They will have a watermark on them.
For any you want to download there will be a link to purchase. I believe they are $15 each. They may offer packages of several at a discount (example, buy 10 and it's only $100), not certain. Since we have an AP we always get all photos included so I've not checked in to pricing in a while.