A function is a building block that solves a small problem. It is a piece of code that has a name and can be called from anywhere else in the program. A function takes parameters and returns a value (optional). Functions are what allows programmers to construct large programs and solve multiple issues one by one. Functions create a more manageable environment for programming as they split large problems into small pieces. It improves code readability and understandability and avoids repeating code. Another benefit of using a function is code reusability as existing functions can be called several times.