Keyboard Shortcut: Create New Item
10107 CTRL+N – The King of Keyboard Shortcuts
Whether you want to create a new email message, add a contact, or schedule a new appointment, you can use the same shortcut key.
If the Inbox is open, pressing CTRL+N will create a new email message.

New Appointment
If the calendar is currently active on the screen, Outlook will create a new appointment. But even in Word and Excel, pressing CTRL+N will create a new Word document or Excel worksheet. Truly a top-tier shortcut!
Independent Shortcuts
Anywhere in Outlook, you can use CTRL+SHIFT+A to create a new calendar appointment. However, it’s not always useful to memorize all these shortcut combinations.

For the Sake of Completeness
I haven’t found a scenario yet where this one is essential to know. But to complete the topic, here it is.
