How does promotion system work

I know that you can only get 1 copy of a character, but I got multiple copies of weapons/wyrmprints. Does that mean that unbind is the only way to improve these and that they're stuck at that star level (like soldier's brand is stuck at 2 star)? Also, does this apply to dragons, I only got 4 dragons from my rolls and none of them were copies. Sorry, the tutorial was kind of confusing for me since this is only my second gacha game after FEH.