Discover where the Yangtze river, one of the longest rivers in the world, begins its 6000km journey. People and places -Physical geography - Rivers Learning Points Rivers develop along a course, which begins at the source and ends at the mouth. Individual streams merge; the smaller one is called a tributary. A Twig Curriculum Film. Delivering key learning points. Get straight to the facts in just three minutes – directly linked to core learning, Twig's curriculum films will fit neatly into your lesson plans.