What does training level 2 mean?

I'm still a little lost on this new training. I love having the arenas and being able to train, but I'm unsure exactly what it means. For example, I have several horses that have gone to "training level 2" in the past couple of days, yet they are still at "National" level.

What exactly does this mean for the horse and how does it pertain to showing?

Thanks!

From my understanding, it has to do with showing luck. Every show horse has fluctuating luck, so it will do better some shows and worse in others. The higher your training level, the better luck your horse will have. I think there are five training levels total.