Question about Crossbreeds

I know I read this somewhere - but what exactly does the crossbreed field mean?

Does it mean our horse is a cross between breed 1 and the crossbreed chosen? Or like, if I have a horse that could be like... an Appaloosa or Appaloosa Sport Horse, do I put one as the breed and the other as a crossbreed?

You are correct for all! The system was designed to have the primary breed (breed 1) and anything it was crossed with in the crossbred field. However, it can also be used in the second way you described - if you have something like, say, a Drum Horse, you could put Drum Horse as primary and the breeds that were used, such as Shire and Irish Cob, in the crossbreeds.

Okay! Now is that something I should do for any and all my horses who may have this? Or is it something I can edit at any time? :) thanks so much

You can edit them at any time so you don't need to do it right away. However, if they are currently entered into any ongoing competitions you can't edit them anymore since you may change the breed and it may no longer be eligible for the class it's in. If the show they are entered in hasn't started judging yet, you can retract them from the class, edit as needed, and then re-enter no problem. If registration for the show has closed and judging has started, then I recommend waiting to edit until after the show is done - if you retract then, you cannot re-enter that specific show anymore.

Hope that all makes sense :)