This part of the formula gives us the probability of getting any k successes in n trials.

For example let "success"="getting a 6" and "failure"="getting anything different than 6" when you roll a die. Suppose you roll a die 3 times independently. The probability of getting 6, anything other than 6, and 6 is (1/6)(5/6)(1/6)=(1/6)²(5/6)¹.

Note that in this case k=2 n=3.