Here is my simple code (CSS added into head for readability):
The user enters a number in a box and presses "Count" and the number is printed on the screen starting with 1, 2, 3, ... up to the users number. My question is that when this runs it does it on a fresh white screen with everything else gone. How do I go about having the output "1, 2, 3, etc" as part of the page itself. How can I not only add it into the page but put it into it's own div or class so that I can control how the output will look?
document.write() should be avoided like the plague. It's only useful during the initial run of displaying the page, and even then there are better ways to do things. Used after the page is initially displayed, it replaces the page with whatever you are writing, as you have seen. Pretend it does not exist.
Rather, investigate DOM manipulation and the use of the innerHTML property.