The concept of writing user stories, as a way of documenting requirements, was introduced and popularized with Extreme Programming, and then picked up by Scrum and several other agile methods. Nowadays, for many agile developers, a project without user stories would be like a world without pizza. Impossible to imagine.
User Stories Applied
The book User Stories Applied, published in 2004 by Mike Cohn, is a landmark publication that has brought together everything the agile movement has learned about this important subject. Mike's book deals with all the activities that people have to perform when writing user stories, like techniques for requirements gathering, defining roles, working with user proxies, and preparing for acceptance testing. Mike also clearly explains how user stories can play a pivotal role in the wider agile project management processes of estimating, planning and monitoring.
Healthy Opinions Applied
User Stories Applied also contains information on difficult and controversial issues, like how user stories relate to user interfaces, nonfunctional requirements, use cases, user scenarios, IEEE 830-style requirements and the horror of the Happy Meal Pizza. OK, I lied about that last one. But it's nice to see that Mike doesn't shy away from some sensitive subjects, offering healthy and strong opinions for his readers.
It seems to me that reading User Stories Applied is simply the best and easiest way to familiarize yourself with user stories. Just about everything I found on the Internet about this topic is neatly covered in Mike's book. It is well written and complete. And best of all, it's easy to finish in just a couple of evenings. Either with or without a pizza.