INSERT INTO – user registration

I am assuming you need to add user to using phpMyAdmin right?
Try this: Video Tutorial
Cheers.

No, that’s not it. I am looking for a line which includes INSERT INTO responsible for adding users because I want to add another line, to add this user to one more table in my database.

To make it clear:
1. User fills the registration form
2. His data must be added to both tables: wp_users and users (table without prefix).

Sorry I don’t know how to do that. ??

I don’t have a great answer for you, but take a look at this:
https://codex.www.ads-software.com/Plugin_API/Action_Reference/user_register
for an example of tying a custom function into the user_register action hook. That hook is found on line #1937, at the end of wp_insert_user() (https://core.trac.www.ads-software.com/browser/tags/4.1.1/src//wp-includes/user.php#L1657).

That hook fires after collecting the user’s data, but you’ll have to see if it has the data you need (read the cautions in the description of the hook). I may be way off here, but you’ll at least learn a lot by reading through the in-line documentation for that function. I did. Good luck!