The calendar not only shows you all campaigns of your brands, you can also work on new and existing campaigns directly in the calendar. The following options are available to you.
Click on a desired day in the calendar to schedule a new activity on that day. Select "Create campaign" in the dialog to start creating a campaign. The selected day is already stored as the start date in the campaign and can be adjusted in the "Runtime" step.
Alternatively, you can click the "+" icon in the upper left corner to create a new activity without a predefined date.
Click on a campaign to edit it.
Via right-click on a campaign in the calendar a context menu appears, in which you can remove the campaign directly.