What is User Story?
A user story is a small, plain-language statement of need from the user's perspective — classically "As a [role], I want [capability], so that [benefit]." It's deliberately not a specification: it's a placeholder for a conversation, kept honest by acceptance criteria.
The "so that" clause is the part teams skip and exams test — it carries the why, which is what lets a team negotiate scope intelligently instead of building requirements verbatim.
Worked example
"As a returning customer, I want saved payment methods, so that checkout takes seconds." Who (returning customer), what (saved payments), why (faster checkout) — plus acceptance criteria on the back to make it testable.