I've heard that MacOSX has Apache and MySQL installed. How do I exactly find the program Apache, I openede ethe system prefs - share, but nothing else comes up about Apache and MySQL. After I find out that, all I need to do is install PHP right?
OSX comes with Apache and PHP. MySQL is not included. PHP is not active by default, you need to edit httpd.conf to get it going (I think).
Turn on Personal Web Sharing to turn apache on. Call localhost or 127.0.0.1 in your browser address to see what your serving up.
Web root is located in /Library/Webserver/Documents/
The conf file for apache is /etc/httpd/httpd.conf
Remember to restart apache after any changes to httpd.conf. You can do this by turning sharing off, then on, or from the command line.
And as Greg said, head over to http://www.entropy.ch/software/MacOSx/ to save yourself the headache of installing MySQL. And grab the PHP binary as well, since it's a more full featured compile.