The words functions and methods are used interchangeably but they are not exactly the same. A function is a piece of code called by its name, meant to do a specific function and can be called at any point, ie. if the function is declared as global, while a method though very similar to a function, is called by an object within a class.
An example of a function: A function to calculate the average of three numbers.
An example of a method: Say we have a class CARS and an object of that class Toyota, a method within the class would be one to calculate the distance car travelled, and this method can be called by the instance of that class Toyota. Assuming the name of the method is Distance(), this will be called as Toyota.Distance()