To better understand the context of the software system, it is very useful to have a simple UML class diagram with all the key concepts (names, attributes) and relationships involved of the problem domain addressed by your module.
Provide information from the event to add or to edit in calendar
Provides the time before the event occurs, the user may want or not to receive the notification
Provides the user information, like the username and password to manage his calendar
Provides settings for managing the calendar, like turn off notifications, change the color of events or calendar settings.