Apache handlers allow you to control what Apache will do with certain pc file types. When Apache recognizes a file, it has an action built in for that file and it will perform that action accordingly. If you wish Apache to do a different action, you will need to make a handler to tell Apache to perform that action. For example, if you use a file that needs a special service to run it, such as a file with server side contains that is not known with a .shtml expansion, you need to tell Apache to treat these files in a different way.
To get regular web-page coding concept websites to deal with php concept, you need to add this line to your htaccess file.
AddHandler application/x-httpd-php5 .html .htm
Note: It is strongly recommended that you never allow html pages to instantly manage php or shtml, because this causes all of your web-page to be processed by the server first. Instead, please relabel your details to .php or .shtml whenever possible.
System Mime Type defaults