Technical Q&A
How to get the logged-in user's id in drupal?
In pre Drupal 8 era, the global variable $user was available every where, from you can easily get the current logged in user id. For all new version of Drupal, you should use
\Drupal::currentUser()->id()
Once you have the user id, you can use the User::load to get the user object.
$user = User::load(\Drupal::currentUser()->id());
Here is an example of retrieving specific information from the user object.
<?php
// Load the current user.
$user = User::load(\Drupal::currentUser()->id());
$email = $user->get('mail')->value;
$name = $user->get('name')->value;
$uid= $user->get('uid')->value;
?>
Reference