1) Register with the site (in the same way you registered on the Gamepark site - with a wizard).
2) Choose your game(s)
3) pay for them (visa, mastercard, etc etc)
4) Download the games for the 'my JoyGP' page. You usually get 5 days to do this from the date of your first download - i.e. if you lose the game or it doesn't download properly, you have another 5 days to download it again (as many times as you need - remember it'll only work on YOUR GP32).