what you need:
1. A deck of card (it doesn't need to be complete)
2. A spectator
what you will do is ask your spectator to pick a card,
secretly you look at the bottom card of the deck while holding the deck in your hands,
then you put the cards on the table and pick up the half of the cards and lay then next to the remaining pile.
now ask the spectator to put their card on the pile you just put down.
now you put the remaining pile on top of it.
now say a magic word or shake the cards and say you are going to find the spectators card.
now you flip the deck so you can see the cards, just spread the cards and look for your card.
the card before your card that you remembered is their card!
Your friends will be stunned!