iN wordpress…I want dont want to allow user to see any page without login

Solution:

header.php is included in each page, you can check with this get_current_user_id(); this function returns 0 if not any user in logged in.

in header.php

<?php 

if( !get_current_user_id()  && !preg_match('/login/', $_SERVER['REQUEST_URI'])){  // checks if the user is not logged in and the page is not login page,
 // redirect to some other page,
 header("Location: ". site_url().'/wp-login/' ); // redirecting to login page
 exit()


}
?>