Hi, Christoph

Are you referring to face-to-face / seminar activities? If so, there are calendar options in the activity's setting that allow you to set where you want the event to be visible e.g. the course calendar, site calendar, or none.

If you set the option to "Site", then the session / event it will appear in the calendar block and users can select it and sign up from the link in the block. By default, events will appear in the user calendar and the user would see an additional event (once signed up), including the original. Visibility of the different context events can be hidden and shown via the main calendar page too.

Does that help?

Cheers.

Tom