After you install the app and setup your account on PrintOps.com, you will be prompted to make a choice of what products you want to connect with PrintOps.com. You can either download ALL products from your store, or choose one or more categories of products. Once these products are downloaded, you will connect them to products on PrintOps.com - but we aren't quite there yet!
It helps to organize your products on your Shopify store into categories - then you can just download the categories you want to connect on PrintOps.com.