Solution
Use a server-side language like PHP in order to generate a full HTML page.
For example, create three files:
- header.php
- page.php
- footer.php
In the header.php file you have to put the first part of the HTML page.
In the page.php file you have to put the main content of the HTML page.
In the footer.php file, like the header.php, you have to put the end part of the HTML page.
So you can change the page file and the header and the footer remain.
header.php:
<html>
<head>
</head>
<body>
<div id="header">
Place your header here.
</div>
page.php:
<?php include('header.php'); ?>
<div id="main_content">
Place your page content here.
</div>
<?php include('footer.php'); ?>
footer.php:
<div id="footer">
Place your footer here.
</div>
</body>
</html>
For more information, search for a PHP tutorial with Google.
OTHER TIPS
In regards to what you see in most websites, they just reuse the same code.. (usually in an external file and insert it in all their pages)..
Take a look at Server Side Includes for more info
Depending on what you wish to display you could look at using divs or using includes.