Enable Server Side Includes in Apache
Server Side Includes (SSI) is a simple mechanism that allow you to add dynamic elements into your HTML file without playing with complicated scripting languages such as PHP or Perl.
To enable it under Apache, add the following lines to the Apache configuration (httpd.conf)
AddType text/html .shtml
AddOutputFilter INCLUDES .shtml
Restart Apache to take effect
# apachectl -k graceful
Now all yout .shtml files be will parsed and SSI related tags will be evaluated.
To see what SSI directives you can use, check out the following document: