1) to see if mysql is installed, just type 'mysql -uroot -p' from the command line. You will be prompted for the password you entered at install time. If you forgot that password, there is a way to reset it but I forgot how.
2) As for apache, just open a browser and type in the IP of your server. It *should* show you the apache default page. leave this browser window open.
3) For PHP, find the web document root folder (it's probably /var/www/html) and put a file in there called index.php and type this in it:
then refresh the browser from step 2 which is pointing to your server's IP. you should get a different looking page that outputs all the php information.