Spanish 21 is similar to traditional Blackjack but with more options and payouts. One difference is that all numbered 10 cards are removed from the deck leaving 48 cards in each deck. Jacks, Queens and Kings count as 10. Aces count as 1 or 11 (whatever is to the Player's advantage).
The dealer must always hit on any hand value of 16 or less and stand on any value above 17. The dealer must always stand on hard 17 but the rule on soft 17 varies from table to table. It has become common for the dealer to hit soft 17 since that increases the probability of the dealer (house) winning.