There are many variations to blackjack, but these will be the rules we will use for this course.
In blackjack you are playing only against the dealer. Your goal is to end play with a hand whose value is as close as possible to 21 without going over. If your hand value exceeds 21, you have lost that round. At the end of the round any players whose hand values are closer to 21 than the dealer's win, and the others lose.
A blackjack is a total of 21 in your first two cards. This is different than a 21 that is made at any point later in the game. A player blackjack beats any dealer total other than a dealer's blackjack, including a dealer's regular 21, and you immediately win. (If both a player and the dealer make blackjack, the hand is a tie.) Challenge: calculate how often you'd expect this to happen (i.e., you get a blackjack every X hands, X=?). The answer is amusing.
Face cards (Jack, Queen, and King) count as 10 points. Aces count as 1 point or 11 points, player's choice. The same ace can be counted as different amounts of points at different times in the same round. All other cards count as their rank value. Suits are not relevant in blackjack.