Note: Before you can start creating sprints, you have to create a Release. See Creating a New Release.
You should have a backlog of stories with enough details for the Scrum Team to understand what needs to be accomplished. Details can be added as the sprint progresses but enough details need to be provided for the team to estimate the amount of effort required.
After a sprint plan has been finalized, the Scrum Team will begin adding tasks to the stories.