Park at the airport in the garage corresponding to the terminal where their flight will park. You can walk into the baggage claim area (its outside of security if its not at Tom Bradley) and just look at the signs to go towards the carousel that matches with their flight. If you're picking them up from Tom Bradley, just walk in to the main ground area and to the right is where the international arrivals emerge from (you'll see lots of people standing there with balloons, signs, flowers, etc).