What does an inverse function do?

A function is a rule by which you take a set of values (called the domain) and map them to another set of values (called the range). An inverse function does the reverse. It takes the range of the original function to form the inverse function's domain and maps these values to the inverse function's range, which is exactly the same as the domain of the original function. You can only have an inverse function if the original function is one-one, i.e. one value on the domain gives a unique value of its range.