The Sprint Backlog is the output of the Sprint Planning, where the Developers select the Product Backlog items that they can deliver in the Sprint and create a plan for how to do the work. The Scrum Guide states that "The Sprint Backlog is composed of the Sprint Goal (why), the set of Product Backlog items selected for the Sprint (what), as well as an actionable plan for delivering the Increment (how)."1 The Sprint Backlog is owned and managed by the Developers, who can update it throughout the Sprint as more is learned. The Sprint Backlog makes visible all the work that the Developers identify as necessary to meet the Sprint Goal.1 Reference:
1: The Scrum Guide2, page 15
2: The Scrum Guide