How to write and call functions in javascript with for loops?

Well you really aren't very far off at all. Actually your solution has all the code you need just some of it is in the wrong place. I would have posted this as a comment but as this is a new work account I can't actually post comments so here is a full solution with the explanations.

Your wall function, while annoying with all the alerts is actually correct and doesn't need any adjustments. With that said you might want to play with parseInt and parseFloat to make sure you are getting valid numbers but I am assuming that is outside of the scope of the assignment.

Now on to your main function.

var num = Number(prompt("give a number of times to repeat, must be 0 or greater"));

This is ok and will prompt the user for a number, once again you might want to test that you got a valid number using the aforementioned links.

var count = num;
  for (var a=0; a<=num; a++) {count++;}
  alert("Stats Solver execution " + num + " ===================");
  if (num===0){alert("done ==================="); return;}
  wall()
  alert("done ===================");

This is where things start to fall apart a bit and where i think you are having problems. So I will break this down line for line and explain what each line is doing and you can compare that to what you think its doing.

var count = num;

Nothing crazy here, you are just creating another variable to hold the value in the num variable. Slightly redundant but not really a big deal.

for (var a=0; a<=num; a++) {count++;}

This is the line that appears to have given you the most confusion. This is the actual loop but inside the body of the loop { .... } nothing is being done except 1 is being added to count (count++). If I am understanding the assignment correctly, inside this loop is where you need to call your wall function after alerting the 'Stats Solver execution .....' stuff. All you need to do is move your function call inside this loop.

if (num===0){alert("done ==================="); return;}
      wall()
      alert("done ===================");

This part is clearly you a little lost and just trying things to get it to work, don't worry even after 12+ years of development i still write code like this ;). You really don't need this as the actual call to wall() will work fine for you.

I am bored and am waiting on work so for the sake of being a complete answer here is an example of how your code should look. Please don't just hand this in rather try and actually understand the difference between what i wrote and what you did because these are some very basic concepts that if you gloss over will make your life much harder down the road. Always feel free to ask, thats how people learn.

function myMain(){
    // get the number of repetitions from the user and cast as a number
    var num = Number(prompt('Please enter the number of times to repeat'));
    // loop from 0 to the number the user provided - 1 hence the < 
    for (var i = 0; i < num; i++){
        // alert the iteration of the loop, you will notice i add 1 to num when we alert it; this is because it starts at 0 so the first time it displays it would show 'Stats Solver execution 0 ======' instead of 'Stats Solver execution 1 ======'
        alert('Stats Solver execution ' + (num + 1) + ' ===============');
        // call your wall function
        wall();
        // go back to the top of the loop
    }
    // alert that we are done. 
    alert('done===============')
}
// your wall function goes here
// call your myMain function to kick everything off
myMain();

Just for fun you might want to look at console.log instead of alert to not make it such an annoying process with all the popups.

If i missed anything or you are confused about anything don't hesitate to ask and i'll do my best to answer.