The Raiseaticket REST API enables secure integration with external applications and business systems. Authorised applications can create, retrieve and update tickets, users, agents, groups and other supported records, so the helpdesk can exchange information with the systems you already run rather than sitting apart from them.
Authorised applications can create, retrieve and update those records. In practice that covers raising a ticket from another system, reading tickets out for reporting or archiving elsewhere, and keeping people and group structures aligned with a system that already holds them.
Connecting the helpdesk to something that already exists in the business - an internal application that should raise a ticket automatically when something fails, a reporting stack that needs ticket data alongside everything else, or a directory of people that should stay in step with your agent and user lists rather than being maintained twice.
No. The REST API is a premium add-on. The free plan covers the helpdesk itself - 5 agents and 500 tickets a month, with SLA policies, reporting and the knowledge base included - and API access sits outside that.
Whoever maintains the system you are connecting to, working with a Raiseaticket administrator. It is an integration task rather than a configuration one: the helpdesk side is authorisation, and the logic lives in the application making the calls.