Jump Start Sinatra: 
This short SitePoint book provides readers with a fun and yet practical introduction to Sinatra, a framework that makes web development with Ruby extremely simple. It’s not intended to be a completely comprehensive guide to the framework or an in-depth Ruby tutorial, but will quickly get you up to speed with Sinatra and give you the confidence to start experimenting on your own.
The book is built around a real-life example project: a content management system. It’s a fun and easily understandable project that is used to demonstrate the concepts outlined in the book in a practical way.
This is a clear, approachable and very easy-to-follow book that will get you to to speed with Sinatra in no time.
