The spectator thinks of any card, generates a random number, and shuffles the deck. That number is dealt to and, in this shuffled deck of cards, it is revealed that their card is precisely at that number. Andrew reveals that the rest of the deck was actually blank. On top of that, the card that they were thinking of was blank too, which means the whole experience just happened in their mind.
White Room is a technique you can use to create a direct mind reading experience using nothing but the imagination. The person keeps their eyes closed for more than half the trick and everyone watching knows that they’re experiencing something special, creating an interesting spectacle. You will always have this with you because it uses nothing but words. Imagine being able to tell a person what card they have arrived at while making every decision secretly in their mind.