The decals are vinyl with a self adhesive backing. I would suggest that after you apply them, you seal the whole airplane with a light weight clear coat.
I read in one of your earlier posts that this was your first bi-plane. It was also my first bi-plane. Mine was destroyed 4 times before I gave up. 20 years later I decided to give it another try.
When you first fly it be ready for anything. The first time I flew the one I have now it was like jumping on the meanest horse in the barn.