Some events are certain, others are not!
Many of the events that occur in our day-to-day life are certain, but some events are such that may or may not take place. For example, getting heads on a coin after tossing it, getting number 3 on a dice, producing a non-defective product in a factory, etc.
It is not possible to predict these events accurately.
The occurrence/non-occurrence of these events depends on the element that we call chance.
'Probability' means to express the possibility of these uncertain events numerically.