You need to have Apache running on your system. Once it's running, open up your browser and type in localhost/test.php in the address bar. This is assuming that test.php is in the correct location.
If you install WAMP, the correct location will be something like C:\wamp\www. In addition, once WAMP is installed you can just click on the WAMP tray icon and then click "www directory" which will open the correct location into which you will place test.php.
If you don't have Apache/PHP installed, you can download WAMP which installs those and MySQL all in one, automatically: WAMP Server