user.php

<?php
// Need to add 'activerecord' to your packages in config.php
namespace Fuel\Application;

use ActiveRecord;

class Model_User extends ActiveRecord\Model {}

welcome.php

<?php
/**
 * Example Usage of the ActiveRecord Model.
 * Associations do not currently work
 */
namespace Fuel\Application;

class Controller_Welcome extends Controller\Base {

	public function action_index()
	{
		$user = Model_User::find(2);
		echo $user->name;
		$user->name = 'Jacob';
		$user->save();
		
		$user = new Model_User();
		$user->name = 'Joe Smith';
		$user->save();

		echo $user->id; // 3
	}
}