If you inspect the snowbound, it will give you the instructions. Basically, it is a container, you put the stuff in it and press combine (no fail).
The container is the snowbound armor item you looted, use it like a normal container and put the other 2 items in it.
I have bought a couple of snowbound armor in the Bazaar and have the emblem and snowbound refined velium to add to them but the armor says container closed.How do you open up the container to add the other two pieces?
The container works just like any tradeskill container/bag. Right-click the container with it in an open inventory slot (Bag Slot), it won't work if it's inside a bag. Then just hit the Combine button and profit =)