Search your library for a Forest card and put that card onto the battlefield. Then shuffle your library.
You can find any card with the land type Forest, including Snow-covered Forest or non-Basic lands like Tropical Island, Murmuring Bosk, or Stomping Ground. You can even find a card that is a land in addition to other types, such as Dryad Arbor.
Because the “search” requires you to find a card with certain characteristics, you don’t have to find the card if you don’t want to.