Other stakeholders are for example customers, users or managers. These roles do not belong to a Team they are 'outsiders'. They are involved or in some form influenced by (not responsible for the success of) the product. Involvement of Stakeholders is the choice and responsibility of the team.
For example, the Product Owner can invite a customer or user to share their expectations of the product or service. This can be done during a Product Backlog Refinements session with customers or during Sprint Reviews. The Development team may invite other Stakeholders to clarify technical issues. The Team Agility Master works on organizational level with Stakeholders who are needed to address impediments, eg. with relevant managers.