In Math, functions play a very prominent role. They determine relationships between numbers in specific sets.
A function generally has a domain, the figures going in. Along with an image, the figures or solutions coming out. Functions can have a number of variables or unknowns.
Math functions can also be graphed and drawn on suitable axis. Some are of course, easier to plot and illustrate than others.
Composition of functions is also possible, where two or more functions work together to form another function. Composition of functions can be a very interesting topic, depending on which functions and specified domains you have to deal with.
Recurrence Relations are a type of function that can be particularly helpful when thinking of money and interest. Which results in what can often be some rather intriguing real world applications.
The study of many topics in Mathematics, often involves dealing with functions in one way or another.