You don't even have to leave Confluence to create a new Outlook calendar.
...
Just
...
click to "+ Add Calendar" button and select the option "Create Calendar" which opens a new modal. Like in the open calendar modal you have the choice between three different tabs:
Personal Calendars
Group Calendars(only shown when using Office365)
Shared Calendars(disabled when no shared mailbox is configured)
Select the desired tab and type in the name of the new calendar and create it by clicking on "Create". After a few seconds the calendar is created and already open.
Now you can directly create new events or schedule meetings.