There is a good chance Apache/PHP/mySQL are already installed on your machine. Many "default" installations install them. If not, there are many directions available for performing the installation. You will have to decide if you want a dynamic module and a few other things. I usually build it all from source.
Any text editor will work for PHP/HTML, but color syntax highlighting really makes things easier. Search the forum here for many good suggestions.
To see if it works place the following text in a file called info.php into your web directory (usually /home/httpd/html) and then browse to it (http://localhost/info.php). If you see a bunch of colorful tables you are ready to rock and roll. If you see a blank page, better go find the installation instructions at <http://www.php.net>.
info.php:
<head><title>PHP Test Page</title></head>
<body>
<?php echo phpinfo(); ?>
</body>
