What you are referring to is often known as a LMS – learning management system. I’ve built one in the past with Drupal for a client. That said there are several options there that would be much more efficient and robust than building your own. One that comes to mind is called Moodle. I’m not in the business of recommending Wordpress but for this type of small website it might be a good option as well. There are undoubtably plugins available to turn a Wordpress site into a LMS with video support. Much like building your own ecommerce system from scratch I think there are much better options out there. I don’t think I would ever recommend building this from scratch for a client without using at least a framework or more than likely an existing content management platform.
I hate to judge others but if you are having trouble with simple things like this you are going to have a very difficult time building a LMS. If you do manage to get it working it will probably be riddled with bugs, poor programming decisions, security issues, etc. All of which can be somewhat avoided by using a framework or existing content management platform.