Say you want to center your navigation on the page:

[code lang=”html”]
<ul>
<li><a href="#">Home</a></li>
<li><a href="#">About</a></li>
<li><a href="#">Contact</a></li>
</ul>
[/code]

Simply tell CSS to:
[code lang=”css”]
ul {text-align:center;}
li {display:inline-block;}
[/code]

And don’t forget to remove any float on those elements, if any.