You can do this with HTML alone using Server Side Includes. Simplest example:
index.html
<html><head><title>Test</title></head>
<body>
<!--#include file="navbar.shtml" -->
</body>
</html>
navbar.shtml
<ul class="nav">
<li><a href="/">Home</a></li>
<li><a href="/about">About</a></li>
</ul>
What you should never do is use framesets or iframes to do this. https://stackoverflow.com/a/15938545/822711
Please note, this will not work using the file://
protocol, it needs to run on a web server as it would in a live environment. This could be on a private or public server, or localhost using a server running on your computer such as wamp.