How do you do probability

That's like asking how do you 'do' speed, or how do you 'do' temperature.

Without a problem or exercise to work on, the best I can tell you is:
Memorize these two formulas, and then use them:

1). The probability that something will turn out right is

        (the total possible number of correct outcomes)
divided by
        (the total possible number of all outcomes, correct or not) .

2).  The probability of TWO different things BOTH turning out right is

         (the probability of the first one turning out right)
times     
         (the probability of the second one turning out right) .