After you have created an appointment you can create a list of participants. To do this you select participants in the upper menu:

Now you have the choice to add individual members or entire groups of members to the list. It is possible to send an invitation to every participant. This is done by an automatically generated e-Mail. The participants then have the choice to accept or decline the invitation. The current status of every participant is displayed and can also be manipulated here. Additionally any information on participants can be added in the text-field.