You may mill three cards. Then return up to one creature card and up to one land card from your graveyard to your hand. (To mill a card, put the top card of your library into your graveyard.)
If you have fewer than three cards in your library, you can't choose to mill any cards this way.
The creature and/or land card you return doesn't need to be one of the cards you just milled. It can be any card that is in your graveyard at that time.