When you sign up for an event (or are signed up by someone else), you will receive an e-mail. This e-mail contains the event's .ics file.
All e-mails containing event data and .ics files are interpreted as event notifications by the common email providers (e.g. Google Mail or MS Outlook). The events should be automatically added to you calendar application.
Please note: Whenever something about an event changes (for example the title, the date etc.), you receive a new e-mail.
This email should automatically update the event inside your calendar. Usually, there is no need to update the changes by yourself.
Please note that the automatic calendar update currently does not work for the event organizer.
If you, as an organizer, sign up for your own event, the .ics file you receive via e-mail will not be automatically added to your calendar.