When you select the Training option on the main menu on the left side of your GMAU student dashboard you'll see options to select Lessons, Classes, and Extras.
Lessons
When you select Lessons, the Lessons page for the rank level you're currently training in will appear. And all the lesson videos for that level are provided on that page.
A "lesson" is a relatively short video (3 to 15 minutes) that focuses on teaching you just one technique or form in the martial art you're studying. In each lesson video, the instructor demonstrates the technique or form in detail to help you learn it correctly and efficiently.
Classes
When you select Classes, the Classes page for the rank level you're currently training in will appear. And all the class videos for that level are provided on that page.
A "class" is a longer video (25 to 45 minutes) that typically takes you through warm-up exercises and/or techniques and forms practice and/or combination drills and/or sparring practice and/or cool-down exercises. It's just like taking a full class at a martial-arts studio or gym. The things you learn in the Lessons are what you practice in the Classes.
Extras
When you select Extras, the Extras page for the rank level you're currently training in will appear. On the right side of that page you'll see several categories to choose from that include Workouts, Training Tips, Live Classes, and more.
An "Extra" is a video that contains bonus material for you to learn from. It helps you train further and progress faster in your martial art.