Blackjack is about getting a better hand than the dealer, ideally 21 ( which is called Blackjack if it is made of one face card and one ace).
First, you two cards and the dealer gets two, one of which is visible. While you can always decide whether to take another card (hit) or not, the dealer must stand at 17 and hit when he get less than 17. Sometimes the casino rule is the dealer may hit on a soft 17. If the dealer hits a card that takes him over 21, you have won – but you have to act first, and you can also lose by hitting over 21 – in which case the dealer does not have to hit any further.
An ace can be counted either as 1 or 11 points. After you have seen your two cards, you have several options:
Hit – take another card now
Stand – no more cards
Split – if you get two cards of same value, you cand split and separately play them (you will get only one more card after that mostly, and you have to make another bet of the same size)
Double – you can double the bet, but then you must buy at least one more card.