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User Stories are used by agile methodologies to capture the functionality that a system or software should support.  For details about what a user story is and how to write one reference What are User Stories.

At the beginning of a project user stories are identified and developed in a story writing workshop – a brainstorming session in which the agile team comes up with as many user stories as possible (the agile team commonly includes some combination of customers, product manager, developers, testes, etc.). Each story is sized and prioritized for the first time.  This prioritized list creates the Product Backlog (Release Backlog).  During the workshop the team selects an iteration length (usually between 1 and 4 weeks) and also the rate at which they will be able to complete user stories (call the velocity), both of which become important when determining how to schedule user stories later in the process.

Many agile methods call for discarding user stories once they have been coded and implemented.  However, agile methods are flexible and adaptive, so the determination of whether to save and maintain user stories typically varies from company to company.  

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