When you are working on your document you may find that you want to change the size that you are viewing the page at or view different numbers of pages at the same time.
With Publisher you can zoom in to the actual area you are working at, view the whole page you are working on to see how everything looks on the page or view a number of pages to see how they look together.
How you view your document will depend on what you are trying to do. You can even decide whether you want to view the rulers and what unit of measurement you want to use.
What do you want to know more about?