Sync never "adds" products. It only syncs the data of existing linked products. Our other customers like to strictly control what items are visible on their websites.
Sync will be automatic once you are live. While you are under construction, sync is manually requested.
There are 2 ways to import products. One is simply to add a product and give it a sku from unleashed as product code. Then the sync will catch up.
Otherwise, use the import from category approach.