The probability of two independent events and are calculated by multiplying their individual probabilities:
Example: the probability of getting a king in a deck of cards is . The probability of getting a card of hearts is . Because the two probabilities are independent, the probability of drawing the king of hearts is: , as you would expect.
Complement is simply one minus the probability of the event. So if is an event with probability , then the probability of its complement is . The probability of getting a 4 on a die is . So the probability of not getting a 4, or the complement of the event that you get a 4 is: .
Hope that helps.