why do we need to learn the formula for binomial probability distribution?

Question

anonymous · Answer

The binomial probability distribution is useful when a total of n independent trials are conducted and we want to find out the probability of r successes, where each success has probability p of occurring. There are several things stated and implied in this brief description. The definition boils down to these four conditions:

Fixed number of trials
Independent trials
Two different classifications
Probability of success stays the same for all trials

anonymous · Answer

An example would be the prob. of getting 3 heads when flipping 3 coins.

anonymous · Answer

how would you use it if you had P(r=3) n=5 P=.735 ?
I know how to do it in my calculator but I dont understand how to plug it in.