What are families of functions and how are they useful?

A family of functions is a set of functions defined by the same type of formula - we can talk about the polynomial family, or 2nd degree polynomial family, or the family of sinusoidal functions. 

Alternatively, we can define a family by a formula that involves the argument and one or more parameters. For each specific value of the parameter(s) we'll then get one function in the family.

Yes of course i will indeed you with your problem.

This makes absolutely no sense at all young man/women