Server side includes are variables that come from the server. You should rename your html pages to shtml if you use SSI.
What if I don't want to use .shtml?
Some common SSI codes:
| <!--#echo var="HTTP_REFERER" --> | 
(referring URL) | 
| <!--#echo var="REMOTE_ADDR" --> | 
(visitor's IP address) | 
| <!--#echo var="REQUEST_URI" --> | 
(requested URL) | 
| <!--#echo var="HTTP_HOST" --> | 
(server name) | 
| <!--#echo var="HTTP_USER_AGENT" --> | 
(visitor's browser) | 
| <!--#echo var="REDIRECT_STATUS" --> | 
(redirect status code) | 
| <!--#echo var="DATE_LOCAL" --> | 
(visitor's date and time) |