Service desks provide a variety of channels for access including:
Phone calls, which can include specialized technology, such as interactive voice response (IVR), conference calls, voice recognition, and others.
Service portals and mobile applications, supported by service and request catalogues, and knowledge bases.
Chat, through live chat and chatbots.
Email for logging and updating, and for follow-up surveys and confirmations.
Walk-in service desk (which are becoming more prevalent in some sectors, such as higher education, where there are high peaks of activity that demand physical presence)., Text and social media messaging, which are useful for notifications in case of major incidents and for contacting specific stakeholder groups, but can also be used to allow users to request support.
Public and corporate social media and discussion forums for contacting the service provider and for peer-to-peer support.
https://www.bmc.com/blogs/itil-service-desk/

The first important step is identifying and managing all the stakeholder groups that an organization deals with. The first and most obvious stakeholder group is the customers, as in service management the organization's main goal is to facilitate customer outcomes. Other examples of stakeholder collaboration include:
Developers working with other internal teams
Suppliers collaborating with the organization
Relationship managers collaborating with service consumers
Customers collaborating with each other
Internal and external suppliers collaborating with each other
The contribution to improvement of each stakeholder group at each level should be understood, as should the most effective methods to engage with them. Depending on the service and the relationship between the service provider and the service consumer, the expectations about the level and type of collaboration can vary significantly. It is important to involve stakeholders, and address their needs at all levels. Determining the type, method, and frequency of such messaging is one of the central activities related to communication.
https://www.bmc.com/blogs/itil-guiding-principles/

Explanation
To set clear business-based targets for service performance, so that the delivery of a service can be properly assessed, monitored, and managed against these targets.
https://www.bmc.com/blogs/itil-management-practices/