Probability is the study of chances or likelihood with the use of statistics. Probability is always expressed as a part of the whole, thereby, in fraction or percentages. The part stands for the number of times that event could happen as reflected in your statistics by gathering data. For repeated trials that only has two outcomes such as flipping of the coin, there is an equation for it:
n!/r!(n - r)! * p^(n-r)*q^r, where
n is the number of total trials
r is the number of success in the trials
p is the probability of the an event happening in one trial
p is the probability of the an event not happening in one trial
In here there are 4 flips, so n=4. If you want to find how many heads in 4 flips, r=4 consecutive heads. Then, p = 1/2 because it could either be a head or a tail, while q=1/2 because p+q = 1. Substituting the values:
4!/4!(4 - 4)! * (0.5)^(4-4)*(0.5)^4 = 1/18 or 6.25%