Card counting in Blackjack helps players gain an advantage by tracking the ratio of high to low cards. The Hi-Lo system assigns values to cards—low cards (2-6) are +1, high cards (10-A) are -1, and 7-9 are neutral—allowing players to maintain a running count to identify favorable betting situations. The KO (Knock-Out) system simplifies this process by using a similar value scale but starts the count positively without adjusting for the number of decks remaining. Both methods enable players to make strategic decisions based on the remaining cards in play.