Creating a node programmatically in Drupal 8? There is much more to it that this, but this is the start...

use \Drupal\node\Entity\Node;

$node = Node::create(['type' => 'CONTENT_TYPE']);
$node->set('title', 'YOUR TITLE');
// Simple textfield
$node->set('field_TEXT_FIELD', 'Your Text Here');
        
$node->save();