What difficulty should you begin with?

There are 4 difficulty levels: beginner, intermediate, advanced and elite.

EVERYONE CAN START WITH THE BEGINNER ROUTINES. Once you master them, start doing intermediate routines. 

Although beginner routines are great for beginners, it doesn't mean they aren't effective for more seasoned trainees. 

Ultimately the difficulty level of the workout is not just based on the difficulty of the movements alone but also on your personal pace and intensity. If you are an advanced trainee, just increase the pace (speed) and weight if necessary and the workouts will become tough.