Look at the top two cards of your library. Manifest one of those cards, then put the other on the top or bottom of your library. (To manifest a card, put it onto the battlefield face down as a 2/2 creature. Turn it face up any time for its mana cost if it's a creature card.)
If you’re playing with the top card of your library revealed, you’ll manifest one of the cards, then the other one will be revealed, then you can choose to put that card on the bottom of your library or leave it on top.
Other players won’t know whether the card you manifest is the top card or second card of that library.