Processing would be turning the field dressed animal into freezer size portions (e.g. like what you'd find in the grocery store at the butcher counter).
Field prep (aka field dressed) would be just removing the entrails and, if it's a larger animal, quartering into a size you can carry out of the woods.
I don't want to post it here in case anyone is squirmish but I'd suggest Googling or YouTube'ing "field dressed elk" so you can get a general sense of what you'd be left working with. You could also ask the outfitter for recommendations on processors as they've likely worked with others to solve the same problem.