To search for a video, there are two areas you can do this.
Main search bar: This will be located on the main homepage, you'll be able to search the title and limit your results by filtering the related subject.
Browse option: This option is available within the top of the page. You'll be able to further define your search by categories. E.g. by movies, subjects, genres, whether it's linked to a category, quizzes and study guides.