Email settings parameters [closed]

I’m trying to create a email login and registration page, I got some code from the internet, what parameters can I put for gmail.

 <?php

//Database details
   define("DBHOST",'localhost');
   define("DBNAME", 'login-system');
   define("DBUSER",'root');
   define("DBPASS", '');

//MAIL SETTINGS
    define("EMAIL", '[email protected]');
    define("SECRET", 'xxx');
    define("MAILHOST", '?');
    define("MAILSECURE",'?'); //or ssl
    define("MAILPORT",'?');
  ?>