When you bet a horse across the board, you are betting on the horse finishing in first, second and third (win, place and show). If the horse finishes first, you collect on all three wagers. If the horse finishes in second, you collect on the place and show wagers. Finally, if your horse finishes in third, you collect on the show wager.
You make three individual bets on one greyhound to Win, Place, and Show. If your selection wins, you collect on all three bets. If your selection runs second, you collect on Place and Show bets. If your greyhound selection runs third, you collect the Show bet.