Simple

Example

The probability of drawing the ace of spades from a pack of cards is 1 in 52 (1.92%) since there are 52 cards in a pack.

The probability of drawing any ace from a pack of cards is 4 in 52 (7.69%).

When an event will definitely occur the probablity is 1.
If an event can never occur then the probability is 0.

The probability of an event ranges from 0 to 1.
The sum of probabilities of all possible events equals 1.

Complement

The complement of an event is the event not occurring
This is denoted by P(A')