(Rails app Api) Send data via HTTP and recieve JSON or XML

(Rails app Api) Send data via HTTP and recieve JSON or XML

I'm building a simple calculator for courier company. This calculator
should recieve some data via http request: weight, origin city and
destination city. Then calculator should send back JSON or XML: price.
Sounds very simple, but I can't find any usable information how to handle
with http request.
As I understand the request should be something like this:
localhost?weight=20&origin="Almaty"&destination="Moscow"
But I have no idea how to handle it with Rails. How to obtain these
variables in HTTP?