User stories serve as a tool in agile project management and software development to articulate how a feature will create value for a user. They are typically written in a format that includes the user's role, the action they want to take, and the benefit they seek. This format often follows the pattern: "As a [type of user], I want [an action] so that [a benefit]." User stories help teams understand user needs and prioritize development tasks to maximize value delivery.