Personal questionnaire using JavaScript prompts
You seem to be on the right track, at least with grasping how to do some basic coding. 

Right now, I only see one major issue: document.write()

document.write() is used to build pages out of javascript, something that is both impractical and ill-advised (in almost every situation). Moving forward, you should start building your pages in HTML and use javascript to tweak the page from that point.

To do this, you will want to replace document.write() with document.getElementById(). Lets look at an example:

You have the following HTML block:

&lt;h1 id='welcome'&gt;&lt;/h1&gt;


Now, to insert text into this block, we would do something like this:

var welcomeElement = document.getElementById('welcome');
welcomeElement.innerHTML = "This is my welcome message!";


There's many things you can do with elements once you have gotten them, but I'll leave that for a later experiment. 



At this point, I'll leave you to learn how to update your code. If you get confused or stuck however, you can view my rendition of your code here: 

http://jsfiddle.net/danthegoodman/v7gLE/