Custom registration field to SQL database

I have created new colums in a SQL table ‘wp_users’. Those fields are
“giodo”, “handel” and “regulamin”.

Don’t add columns to Core tables. There is no guarantee that these won’t be destroyed or corrupted on next update. What you should be using is user meta, and in fact that appears to be what you are actually using:

add_action('user_register', 'myplugin_user_register');
function myplugin_user_register ($user_id) {
        if ( isset( $_POST['giodo'] ) )
        update_user_meta($user_id, 'giodo', $_POST['giodo']);
}

So the question is a bit confusing.

Your code should have already inserted data into the database, just not where you are trying to put it. Your code should have inserted the data into the $wpdb->usermeta table and can be retrieved using get_user_meta(). That is what I would suggest. Abandon the attempt to add columns to a Core table and use the user meta API, which is what it was built for.