Card counting in Blackjack gives players an edge by tracking the ratio of high to low cards remaining in the deck. When the count favors the player (more high cards left), they can increase their bets and adjust their playing decisions, such as standing or doubling down, since the chances of drawing a strong hand are higher. On the other hand, when the count is unfavorable (more low cards), players might bet smaller and play more conservatively. By modifying basic strategy according to the count, card counters can shift the odds in their favor. However, it requires skill, concentration, and practice, and casinos are often vigilant about detecting card counters.