Look at the top four cards of your library. You may reveal a creature card and/or a land card from among them and put the revealed cards into your hand. Put the rest on the bottom of your library in any order.
If one of the cards is Dryad Arbor (a creature land card), you may reveal Dryad Arbor and another land card or Dryad Arbor and another creature card.
You may reveal a creature card, or you may reveal a land card, or you may reveal both a creature card and a land card.