You can access the trainer from the Goals menu (Pro Drums > Pro Drum Trainer > Pro Drums Lessons) or the Training menu. These are actually legitimately challenging beats and will give even experienced drummers some difficulty. One thing that might help is moving the cymbals around, monkeying with the inputs to give a more comfortable drumming experience. Even then, the speed of these lessons, fills and beats are very challenging. You will need to pull them off at full speed to get the achievement.