If you want to buy anything from GOG, then you'll need an account. This is just a standard signup. Submit an email and pick an account name. Then log in and start browsing their shop. When I looked through their catalogs, I decided to join a number of other customers and buy Freespace 2 and Fallout 2. Each game was only $6.99 and they are patched to the latest official release. Fallout 2 even had the unofficial patch to add children back into the game, so it was already good to go.
The purchasing process is simple. You can browse the store by genre, by popularity, by rating, or name. Each game has a number of reviews and a good product description. If you want to buy a game then you just add it to the cart. They have options for Paypal purchasing, which I chose. A quick payment screen later and they were attached to my account.