As htaccess was mentioned as a tag, it would be assumed your using Apache
paste this into it
Options +FollowSymLinks
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule . - [L]
RewriteRule ^$ index.php [QSA,L]
RewriteRule ^(.*)$ index.php?id=$1
so given mysite.com/about - about becomes the value of $_GET['id'] in PHP
In index.php do as you please with that variable - include($_GET['id']); or run a case on it or ...
"Roughly" how Wordpress works. index.php responds to everything; all files / pages / blog posts are handled by index.php and it's functions / classes.
Any href's link to it as above - "/about" or "/contact" or "/products"