It depends on what issue you're having. Generally, a "LoadModule" line, here's one from 'Nix.....
LoadModule php4_module libexec/apache/libphp4.so
....an "AddModule" line, again from 'Nix.....
AddModule mod_php4.c
...and an "AddType" line
AddType application/x-httpd-php .php .html
Note that this server is also parsing files with an .html extension to see if they contain PHP code.
If you want index.php to be the 'home' page instead of index.html, that's in httpd.conf, also.
Now, a disclaimer, you're on Windoze, so probably none of this is even remotely your issue. But it could be. Have you read the "Install" chapter of the PHP handbook at php.net? Also, what exactly is it that's not working, IOW, a more specific complaint might give us out here a clue.....