A team is made up of at least 3 roles: Product Owner, Scrum Master and Team Member. There should be only one Product Owner and one Scrum Master, however there may be more than one Team Member. While these roles are usually carried out by individuals, it is possible to have a single member of the team participate as more than one role. However, it is best practice to keep these roles separate.
As a Product Owner, it is your responsibility to identify and prioritize the specific goals for the project.
As a Scrum Master, it is your responsibility to help keep the project moving along by coordinating with the Product Owner, and helping to resolve anything that blocks the Team Members from doing their work.
As a Team Member, it is your responsibility to perform the necessary work to achieve the desired goals prioritized by the Product Owner.
Sometimes there are people who need to participate on a project at a greater distance. Scrumly provides several roles to help accommodate these various situations.
You can think of a Client as a Product Owner at a distance. It was designed to allow access to the project where more control is maintained by the team. It can be good for situations where the role of Product Owner would be a person external to the company or main group, such as in consulting.
Many organizations have individuals who need to be aware and maintain some oversight of specific projects, but do not need to participate in those projects very much. A Stakeholder role will allow general oversight and limited involvement with the project.
When you need to have someone who can access the project, but does not need to participate, an Observer role is just what you need. These users can view and navigate some of the high-level information in the project, but won't have access to the fine details.
Being able to perform administrative actions like managing teams and editing project details is sometimes needed to be delegated to other people on the team. This can be done by assigning a user to the Project Administrator role. While this role can provide users with much broader access and controls, it does reduce the benefits of having specific roles and focus on actions associated to their logical role on the team.