Conditional Probability is the probability of an event given that another event has
already occurred. For instance, probability that the card is a queen, given it is a heart.
$$P(Q|H) = \text{probability that Q will occur, given H has occurred.}$$
$$P(Q│H)=(P(Q∩H))/(P(H))=(1/52)/(13/52)$$
This implies:
$$P(Q∩H)=P(Q│H)×P(H)=P(H│Q)×P(Q)$$
