This is a simple website.
We have a number in mind that is the "winning" number. The site has a box in the middle of the page that allows poeple to enter in a number between 1 and 1 million. If they guess the wrong number, that number shows up on the website as already guessed. If they guess the "winning" number then the website displays a message saying "you win" or something simple. If someone guesses the right number then no more guesses are allowed.