USPS API + Rails: How to get started?

I'm working on a web store for my company. Right now we do most of our t开发者_如何学编程ransactions through eBay, but we are wanting to build our own web store so as to avoid having to pay eBay's fees.

I've registered with USPS for API access and I've downloaded the technical documentation, but I'm a little lost. I'm fairly new to Rails, and I have no idea how to send the data to the USPS server.

So, where do I start?

EDIT: The API that I am going to be using most is the Shipping Calculator API.

Use this gem: https://github.com/FotoVerite/awesome-usps