The top card of the pack is turned face up to show it to the spectator and then turned face down, removed from the top and replaced in the centre of the pack. David then squares up the deck, clicks his fingers and the card is shown to have returned instantly to the top of the deck.
This trick uses mastery of a sleight of hand known as the double lift. This particular sleight of hand is one which does require considerable practice to perform it slickly and without any tell-tale hesitation but the investment of time and effort is well worth it as it can be used in innumerable card tricks. You can learn how to perform the double lift sleight here.
When the David Blaine is apparently showing the top card, he is in reality performing a double lift to show the card that is really second from the top of the pack. The magician then simply removes the actual top card and places it in the centre of the deck thus leaving the card which he has already shown, on top of the deck. This process can then of course be repeated ad infinitum or the shown card can then be revealed at a time in any way that the performer wishes. This is a fantastic effect in the hands of a master card manipulator such as David Blaine.
Here is another video which demonstrates the basic principle of how any card in any ordinary deck can be made to look as if it jumps to the top as if by magic. Although the quality of the video is a little poor, this guy explains himself and what he is doing well enough. Have fun with this superb card trick but don’t forget that the more you practice the double-lift, the better you will perform this trick.