The basic approach statistical methods adopt to deal with uncertainty is via the axioms of probability:
Probability = (number of desired outcomes) / (total number of outcomes)
So given a pack of playing cards the probability of being dealt an ace from a full normal deck is 4 (the number of aces) / 52 (number of cards in deck) which is 1/13. Similarly the probability of being dealt a spade suit is 13 / 52 = 1/4.
If you have a choice of number of items k from a set of items n then the formula is applied to find the number of ways of making this choice. (! = factorial).
So the chance of winning the national lottery (choosing 6 from 49) is to 1.