Hi Joseph,
The short answer is yes or you will lose all or most style/format. It is not difficult to learn and in the long run using CSS makes code changes much easier.
For information on CSS:
http://www.w3schools.com/css/The w3c site has lots of good information on html, CSS, etc.
If you google vertical menus you may find a menu already to go; I just did a quick search to get you started.
Kerry