Counting cards in black jack means counting the number of cards played in previous hands that are of a certain value range. Example: knowing that a large number of low value cards valued (2-6) have been played, means there is are many more high value cards (9-10) still in the deck. With this knowledge it would be wise to increase your bet because, should the dealer's cards total less 17 he/she must take another card and will very likely bust. You are not required to take that risk and can hold with as little as a 12 point hand. Double down if you are holding a 10 or 11 points, as it should also pay off. The casino will counter this situation using multiple decks and frequent shuffling when their count shows the advantage has shifted to you. while the dealer is forced to sit back and watch. Maybe this site
Poker - Jeux Poker will help you to know more about counting of cards.