Get field value of a Node / Entity

Methode 1 : Example:

$value = $node->get($field)->value;

$target = $node->get($field)->target_id; // For entity ref

Methode 2 Example:

$field = 'field_thefieldname';

$index = 0;  

$a = $node->toArray();

if (isset($a[$field][$index]['value'])) {

    $value = $a[$field][$index]['value'];

}

Example 3 : Get / Render image (Show current user's picture)

$userCurrent = \Drupal::currentUser();

$user = \Drupal\user\Entity\User::load($userCurrent->id());

$renderd_image = $user->get('user_picture')->first()->view();

Or for multiple values

foreach ($node->get('field_images')->getValue() as $key => $image) {

    $image = $node->field_images[$key]->view($settings);

}

//Example Of $settings

$settings = ['settings' => ['image_style' => 'thumbnail']];