Outlook 2016 for Mac currently doesn't support the CalDAV or CardDAV Internet standards. This means that it's not possible to synchronize your iCloud Calendar or contacts with Outlook 2016 for Mac.
However, Outlook 2016 for Mac supports Apple iCloud Mail. To configure your iCloud email account in Outlook, follow these steps:
In Outlook, on the Tools tab, click Accounts.
In the lower-left pane of the Accounts box, click the Add an account button, and then choose New Account.
Enter the email address and password, and then click Add Account.
Unless you receive an error message, your new account should be set up.
Troubleshooting the “Unable to sign in. Try again or create an app password for this account.” error message
If you receive the error message shown above, try the following:
Create an app password by following the steps in the following Apple article: Using app-specific passwords
Copy the app-specific generated password.
Enter the new password and click Add Account again.
Tip: After you add the account, it appears in the top left pane of the Accounts box, and Outlook begins downloading your messages.
For more information about passwords, see Add an email account to Outlook.