handling concurrent requests and race conditions is rails using redis

I am building an application with ruby on rails as a part of a hiring process. This is my first time using ruby or rails.
It's required to handle concurrent requests while saving to DB i.e.: if the server is hosted on many machines and they sent requests simultaneously it should be correctly ordered. I thought to use Redis as a queue to store requests and handle them one by one, but unfortunately, I did not find enough resources or tutorials on how to implement that.
Can someone explains how this is implemented or show me a better way to achieve the requirement?