If you put a semicolon at the end of this line, then it becomes a function prototype. It tells the compiler/linker/whatever that you will be using a function by the name of My_Name_Is which takes no parameters and doesn't return anything.
//This needs a semecolon after the ), too
My_Name_Is() //Calls function that prints user's name
You could put the definition of My_Name_Is() here. Just rewrite the prototype, leaving the semicolon off this time; type opening and closing braces; and within the opening and closing braces type whatever code you want to use to print your name. Some people don't use function prototypes and just type the definition before main(). Either way works.