Each product you create, subscription or one-time, has three options for shipping rates: Automatically Calculate, Free, or Flat Rate Shipping.
Automatically Calculate with USPS: This option is currently for US shippers only. If you've configured your product to automatically calculate the shipping rate, we will use your ship-from address, product shipping weight, and shipping destination to have USPS return the shipping cost on checkout. It's important to ensure the weight entered on your product is the weight that your shipment will be, so you charge an adequate amount in postage.
Free: This will allow your product to have free shipping, so long as there are no other matching rules under Settings > Shipping. For example, if you have a product with free shipping configured on the product-level and a Canadian shipping rule under Settings > Shipping, any customer who purchases the product with a Canadian shipping address will be charged the Canadian Rate.
Flat Rate Shipping: Flat rate allows you to define a set rate for your product. This is useful if you've averaged your shipping cost and want to charge one rate to all your customers.
You'll find product-level shipping settings under Subscription or One Time Products > Select product then navigate to the Shipping Options Section at the bottom of the page.
To create multiple shipping rates by Country, check out this guide: How Can I Set International or Global Shipping Rates?