This is actually really simple.
open your joomla database in your db manager. I generally do this in "PHPMYADMIN".
From there open the table "jos_users" and then add your additional fields that you require.
Then you go into libraries/joomla/database/table/user.php and declare you variables. So if you added a country field then you declare the variable like so:
var $Country = null;
The next step in the process is editing the actual registration form. This is done by going to components/com_user/views/register/tmpl/default.php.
I don't recommend copying and pasting the current form fields I have ran into issues when i have done that. Also note that everything you edit is case sensitive.
Feel free to PM me if you require additional assistance.
