For the 21+3 side bet, a player will win if the two face-up cards and the dealer's face-up card include: 5:1: Flush with non-numerical sequence cards same suit. 10:1: Straight with 3 cards in numerical sequence other suits. 30:1: Three of a Kind, 3 identical cards, other suits.
Top 3 is a second optional proposition wager with 21+3, where you can receive large payouts on a three of a kind, a straight flush, and three of a kind suited. See posted paytable for payouts and minimum/maximum betting limits. Top 3, just like 21+3, has no effect on your main blackjack bet.