You'll reveal cards until you find one that shares at least one creature type with the creature you sacrificed. For example, if you sacrificed a Cat Wizard, you'll stop if you reveal a Human Wizard or Cat Soldier.

If the sacrificed creature has no creature type, no card can share a creature type with it.

Compare the revealed cards to the creature as it last existed before it was sacrificed, not to the creature card as it exists in its owner's graveyard, to determine which card from your library you put onto the battlefield.

If you don't reveal a creature card that shares a creature type with the creature you sacrificed, you'll just reveal and randomize your library.