In case you want to upload products to a specific collection you have to create a collection first (click here to see how it is done). Once you have created a collection you can upload products to it by adding one or more collection IDs to the column "Collection IDs" in the product upload file.
These are the steps to find the ID of your collection:
Log into your buyingshow.com account.
Go to "MY COLLECTIONS" in the menu on the left side.
3. In column "Collection ID" you will see the ID number of each of your collections.