During the second phase of Sprint Planning, the aim is for the Development Team to determine how they will complete their Sprint Backlog. 

Starting at the top of the Sprint Backlog, you should consider how you will implement the User Story. To do this, use post-its and sharpies and break down the User Story into tasks. A lively discussion among your Development Team should ensue as you discuss how to implement this User Story. Write each task on a post-it note. Attach all tasks to the story.

Once one User Story is complete, select the next story from the top of the Sprint Backlog and do the same. 

You should consider the Definition of Done (DoD) as you perform the task breakdown. You don't need to explicitly state items on the DoD as tasks. Instead, you should post the DoD on your Scrum Board so that your team can reference it and ensure they're following it as they implement the Sprint Backlog.

This phase is complete when the team has broken down all the stories into tasks. Your Scrum Master should count the total number of tasks so that they can create the Sprint Burndown chart.