use vector mask tutorialOk so 2 ways to do this (there's more actually, but these are easiest to explain):
#1- if the vector mask has a white background than define the vector mask as a brush, create a new layer and use the brush, drag the layer onto your deco document (the thing where your deco base is lol). Use the Move Tool to move it into the correct place.
#2- If the vector mask has a transparent (see through) background than drag the layer onto your deco document. Use the Move Tool to move it into the correct place.
If you want to learn how to fill in a vector mask: