Catching a Shopify WebHooks in a Rails App

I have a rails app that sends the user over to Shopify to process the purchase of the product. I want to use their webhooks feature to track when those products have been purchased.

So my question is: Does anyone know what the receiving end should look like? Or does anyone have a sample they would be willing to post?

Second question: How can I simulate this on my local machine so I can develop this before trying to go live.

I have tried to find something on the web and found nothing yet. I have tried to build a simulator but failed. I am over my head here and could really use some help.

--Will Merrell