Which hook/action/filter show User ID of current user

Right now, i try to make a popup windows every time a member login. I need to show particular information on the popup window everytime login attempt succesful. I try to add meta user info which has value true everytime the popup show. So the popop only show once on login session.

Now, i need help. I need to delete the metadata or chage its value into FALSE everytime any member login. how do i do that (before set_current_user hook) ?

I need to know when is the current_user->ID has value. or how do i retrieve username / password ? so i can use this code

global $wpdb;
$user = $wpdb->get_row($wpdb->prepare(“SELECT * FROM $wpdb->users WHERE user_login = %s AND user_pass = %s”, $name, $pass));

i hope i don’t confuse you.