how to link a page url to wordpress

how to link a page url to wordpress

I'm new to WordPress, I just converted my HTML to WP Theme, but now I'm
facing a problem, I couldn't get to work the linking of pages.
The structure of my theme:
index.php
header.php
sidebar.php
footer.php
services.php <- other page in the site
Here's the sample code from index.php:
<div id="menu">
<ul>
<li><a class="current" href="#">Home</a></li>
<li><a href="<?php
bloginfo("template_url")?>/services.php">Services</a></li>
<li><a href="<?php
bloginfo("template_url")?>/services.php#freequote">Free Quote</a></li>
<li><a href="<?php
bloginfo("template_url")?>/customers.php">Customers</a></li>
<li><a href="<?php bloginfo("template_url")?>/about.php">About Us</a></li>
<li><a href="<?php bloginfo("template_url")?>/contact.php">Contact
us</a></li>
</ul>
</div>
</div>
But whenever I try to go to services, it's giving internal server error. I
don't know why it's happening. I really need help. Thanks in advance :)