Can you explain the card trick that is explained here?
Edit: Here's a summary of the trick as explained in the video:
Start by asking a spectator to pick any three cards they like out of a standard 52-card deck, without showing them to you, and write them down (to make sure they won't forget them). (Ed. note: You can shuffle the deck if you like, or even let the spectator shuffle it, but you don't have to.)
Divide the remaining cards into four piles, so that first pile will have 10 cards, the second and third piles will have 15 cards each, and fourth pile, set aside, will have the remaining 9 cards.
Now, tell the spectator to put the first card they picked on top of the first pile, then cut the second pile anywhere they want and put the top half on top of the first pile (and the card they picked). Then they should put the second card they picked on top of what remains of the second pile, cut the third pile anywhere they want and put the top half on top of the second pile, and finally put the third card they picked on what remains of the third pile and place the entire fourth pile on top of it. (Ed. note: You could have the spectator cut the fourth pile too, if you wanted; it shouldn't matter as long as all nine cards of it eventually end up on top of the third pile.)
Now collect the three piles of cards together so that pile #3 ends up on top of the deck, pile #2 in between and pile #1 on the bottom. Next, take four cards off the top of the deck and place them on the bottom. Deal the cards from the top of the deck alternatingly into two piles, the first pile face up and the second pile face down. Tell the spectator in advance to say "stop" if they see any of their cards in the face-up pile (which they won't).
Once you've dealt out the entire deck, set the face-up pile aside, pick up the face-down pile and repeat the process, dealing it into two smaller piles, the first pile face up and the other face down. Again, tell the spectator to say "stop" if they see any of their three cards in the face-up pile — they won't. Keep repeating this process until you're down to just three face-down cards. Show those cards to the spectator; they'll be exactly the ones they picked and wrote down.