You need a templating solution, and PHPlib is probably the best one available for PHP.
Go to http://phplib.netuse.de/index.php3 and get PHPlib.
Stick the template.inc file into your include directory.
Basically, it works like this:
You have a template file (an HTML file that defines the general look and feel of you site).
That template file has places where content will be replaced from your db, which are defined as follows: {title} or {body} etc.
When you create files for pages on your site, include template.inc, call the correct HTML template file, get the content from your database, and assign that content to the template content replacement strings (the {title} etc.).
That's a real breif overview, but I got it to work and I'm an idiot newbie, so you should be able to as well.
-john