How can I transfer my contacts from iPhone to MacBook?
The iCloud method: In my iPhone when I got to Settings -> My Name -> iCloud -> Contacts. The "Contacts" is already on, and I don't know what to do next.


You need two devices to sync. So on Mac too, in System Preferences > iCloud, turn on Contacts sync.

Check Contacts.app > Preferences to see that account is enabled. 

I don't know about iTunes method. 


  so that I can manage duplicate contacts.


That is not easy on Mac either. What I do is: 


On Mac, export all contacts in a vcf file. 
Upload it on https://contacts.google.com and then let it find the duplicates. 
Sort out the duplicates locally and verify it again.
Select all contacts on the Google web interface &amp; delete them.