The three tools have distinct purposes and users, and it’s worth noting their differences before moving on to the integration itself.
Jira Software is specifically designed for software development and IT teams. It organizes work following Agile methodologies, and allows for sprint planning and Release Management.
Jira Work Management is also prepared to manage work, but is aimed at teams other than developers. It has a simplified set of Project Management features (like workflows, task tracking, and collaboration tools). It's often used by Marketing and HR teams.
Jira Service Management supports the activities of IT and service teams related to managing service requests, incidents, and changes. It follows the ITIL framework and includes self-service and SLA capabilities.