Can somebody help clarify/simplify Functions within Functions

/*  I would not call this a simple explaination
 or even an explaination
 I just went through and commented
 what I thought everything was doing */

/* this is one way of doing this*/
/* write a fn with a parameter*/

function say(somethin) { 
    console.log(something)
}
/*call the fn, pass in an argument*/
say("Hello");

/*...................................................................*/

/* this is another way */

function exec(func, arg) { /* I'm thinking that exec is a built in fn ecma6?*/
    func(arg);
}
/* exec is called here, the say fn is passed in as the first param*/
/* the second param is the string that say will print to theconsole*/
exec(say, "Hi, there");

/*.....................................................................*/

/* pass a fn into another fn*/
/* here, an entire fn is passed in*/
exec(function say(somethin) { 
    console.log(something)
}, "Hi, there") /* the string argument is passed in at the end*/

/*.....................................................................*/

/* make it an anonymous fn*/
/* it looks like this fn calls itself*/
/* it's anonymous because it is not named*/

exec((somethin) => { /*2: here*/
    console.log(something) /* prited to the console here*/
}, "Hi, there") /* 1: this string is passed*/