create a basic game

Hi,

I'm hosting a small party, and the idea is to create a very easy small game and send it to some friends, so if they finish the game they recieve a code or something like that so they can open a secured document that will be the invitation(wich I will send them in advance) or something like that, However I don't know a lot of computer programs so I really don't know where to start. Is there anyone who knows how i can make something like that or who has a game I can use for this? thanks in advance!

ps: sorry for the bad english