Talking about Spanish 21 rules firstly we must state that this game is played with six or eight Spanish card decks (48 cards in each, except 10's). In such type of deck the player edge and the dealer edge are balanced with bonuses and beneficial rules.
Important that there are a lot of Spanish 21 variations all over the world and that's why the rules of Spanish 21 game will vary for sure. But the regular rules are the next (in players favor indeed):
Spanish 21 rules offer an optional side bet named "Match the Dealer" as well. In regulation with blackjack rules the player wins concerned bet having the rank of his one card or both cards which suits the rank of the dealer's up card. On six-deck game such matching pays 4 to 1 (3 to 1 while eight-deck playing). And a "perfect match" of suit and rank pays (just imagine) 9 to 1 on six decks and 12 to 1 on eight decks. Also you can win on both hands.
Described side bet contains a house edge of 3% (roughly) and it's much higher than the main game's edge. Even so it's one of the lowest house edge of a side bet in any blackjack card game.
Only after theoretical mastering these Spanish 21 rules you will be able to practice your blackjack gaming at the casino table.