Proper way to work with wpdb to get user’s firstname

You should’nt really be using wp query here, use get_user_meta();

Example:

$first_name = get_user_meta(2, 'first_name', true);

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)