Add groundhogg tag

functions.php

add_action( 'wplms_submit_course', 'add_a_tag_when_complete_course', 10, 2 );
function add_a_tag_when_complete_course( $course_id, $user_id )
{

	if($course_id !== 1500)
		return;
	$tags_to_add = [ 'Course1Complete', 'Course2Prospect' ]; 
	$contact = \Groundhogg\Plugin::$instance->tracking->get_current_contact();
	if ( ! $contact ){
	    return;
	}
 
	$contact->apply_tag( $tags_to_add );
 	
 	$user = get_user_by('id',$user_id);

	$first_name = $user->first_name;
 	$email = $user->email;

	$contact = new \Groundhogg\Contact( [   
    	'first_name' => $first_name, 
    	'email' => $email
	] );
 
	$contact->apply_tag( $tags_to_add );
}

Not sure $contact = \Groundhogg\Plugin::$instance->tracking->get_current_contact() what this line does.