In the free version, we have it setup without using api so it does not calculate shipping (just leave api key and api secret blank). We use fixed shipping plugin for a flat rate and it works well for use.
If you want to calculate the shipping based off provider, you must have the api keys and at minimum a weight for the products. Then in ship station you choose your provider's and types of shipping you want to provide to the customers. Then this will return in the cart for them to choose or in the estimate shipping.