It just won't do anything that can be seen or heard. Only a computer will love it. A function is a piece of code that performs a task. A C program is basically a collection of functions. Functions are called by other functions, which means a service is being requested which is provided by the called function.
Functions can return something to the caller, perform a process or both.
Functions can also accept arguments inside the parentheses following the function name. That's true of any function. The code belonging to a function is placed inside curley braces. We will make it return an integer that is what we send it squared. Before we use it however, we must describe it.