Find the conditional probability of the second event, given the first event. For example, suppose you are drawing cards from a deck, without replacing them, and suppose an event is drawing a heart. Then you need to find the probability of getting a heart on the second card, given that you got one on the first. If the first card is a heart, then there are 51 cards left, of which 12 are hearts, so this is 12/51.
Find the probability of the first event. In the example, in a full deck, there are 13 hearts and 52 cards, so this is 13/52 = 1/4.
Multiply the two probabilities. For example, 1/4 * 12/51 = 12/204 = 3/51.