Look at the top three cards of your library. Put one of those cards into your hand, one into your graveyard, and one on the bottom of your library.
If there are fewer than three cards in your library, look at all of the cards in your library and follow the instructions in order. For example, if you had only two cards in your library, you would look at both, put one into your hand, and then put the other one in the graveyard.