When Goblin Matron enters the battlefield, you may search your library for a Goblin card, reveal that card, and put it into your hand. If you do, shuffle your library.
4/10/2004: 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.
1/4/2008: You can search for any card with the creature type Goblin, including Creature or Tribal cards. Older cards of type “Summon Goblin” and “Summon Goblins” also count. You can’t search for cards that have Goblin in the name but don’t have the creature type Goblin.