You need to assign story points to each story before you can organize the stories vertically into releases or sprints. That's because your team will have a limited timeframe to complete the stories assigned to each release, and usually two-weeks to complete a sprint.

Should story points be assigned to tasks?

The story points estimation on tasks might be the choice of few organizations or projects. In Agile methodology, estimations at story level are advisable and a Sprint is not reviewed at subtasks level but by the story completion level.

When should user stories be estimated?

You do the estimate of the user stories in the PBI's when you have prioritized the items and are done with story point estimates as discussed above. 1. Product Backlog estimation (Story level) - You must do the estimate of at least 80% of the PBI's before we start the first sprint.