Does Shopify negotiate USPS shipping rates or do we calculate our own?

[InletLife]

I am new to Shopify and trying to get my site up and running to sell y products.  I have a question regarding shipping rates.  Has Shopify negotiated a rate with the USPS for shipping?  When I go into set up shipping rates, there is a rate already set/listed under for the United States Postal Service or do I need to calculate my own rate based on my fullfillment location I am shipping from?  

[Summer]

Hey, @InletLife! Welcome to Shopify Community!

We have a feature called Shopify Shipping that allows you to connect your store to Shopify's carrier accounts when you're based in the US (also Canada, Australia, the UK, France, Italy, and Spain). With Shopify Shipping you can take advantage of the following benefits:

• buy and offer shipping labels at discounted rates
• display calculated shipping rates, instead of flat rates, to your customers at checkout
• buy and print shipping labels directly from your Shopify admin

The USPS services you're seeing in your shipping settings are Shopify Shipping rates. If you're happy to use the discounted rates, you're welcome to use and offer them to your customers, however, you also have the option to create your own flat rates if you prefer.

To help you decide what the best shipping setup is, I recommend reading this blog post about various shipping strategies: Shipping Strategies: How To Offer Free, Flat Rate, and More. If you have other questions, don't hesitate to let me know!