There are mainly three roles that a Scrum team have:
Project Owner - who has the responsibility of managing product backlog. Works with end users and customers and provide proper requirement to the team to build the proper product.
Scrum Master - who works with scrum team to make sure each sprint gets complete on time. Scrum master ensure proper work flow to the team.
Scrum Team - Each member in the team should be self-organized, dedicated and responsible for high quality of the work.