Applying a section of a template to an event automatically invites those people to the event. As well as being able to view the structure via the Host-Guest Events icon you can also view host details on the Event Contact Details screen.
From the Event Contact Details screen you can associate a single contact or a selection of contacts to a host. For example, if you have created a group and have invited that group to the event you might want to assign all of those contacts to the same host. A template must have been applied to the event before you can associate any contacts with hosts.