World Search is built into the basic UI and does not recquire an Addon. Use the BACKSPACE key on your keyboard to open the World Search interface.
Click inside the black box to the left of the word "Search" and enter the name you are looking for. This can be an NPC, monster, or object name (but harvest resources cannot be search for). Don't forget, you must type it in proper Upper and lower case, exactly as it appears in-game.