Levels in dressage?

[Lonewolf]

I'm just now starting to actually event (in events besides gym). Anyway, I've been buying random horses who I think will do okay in events. I was putting my pony in dressage events and I noticed that some of the events said level test. Didn't really pay much attention to it. Then I clicked on a different event and it said fourth level or something like that? Can someone explain the difference between them and how you would get horse to other "levels"? Thanks. By the way, here's the pony.

[Alabama]

It is just the difficulty set for that event. You really don't train any differently and some people even say it doesn't matter.

[Lonewolf]

But it wouldn't let me enter it. Maybe I didn't notice that it was limited to a certain breed type or something. Ok, thanks.