Setting up preSave Validations

I need help.  I have scoured over countless posts/articles/how-to's, and I still can't figure this out!

I made a 6 page form with almost every field required.  It doesn't matter if they don't go in order, they just have to enter information before saving.

Fields are: text fields and radio buttons; no check boxes.

I found out that there is nothing preventing a user from saving an incomplete form.  Fine.

I found out how to make a pop-up alert when they click on a field and then click off, leaving it blank. Awesome, but ONLY if they first clicked on that field.  If they completely skip over it, not so awesome.

How do I make a message pop up when they save to ALERT them that they missed something on the WHOLE form?

In all of my research, I found stuff that points to preSave validations, but no one has ever explained the steps on going about executing this.  I have even found a post talking about executing an Action Script with a button, but it doesn't seem to work.

This form will only work if the required fields are actually ENFORCED.  Even if I have to add a button with JavaScript to enforce this message, I need someone to tell me what to do.  I've followed the steps for every other ActionScript needed, but I can't find this one.

Thanks.